[N8VEM: 16673] New N8VEM not running - please help!

[Werner S]

Hello!

I need help with my new N8VEM. While I had no trouble building it, I cannot
establish a serial connection.

After triple checking everything (e.g. successfully continuity testing the
whole board) I narrowed it down to the Z80 /IORQ line (Pin 20) not
strobing. /MREQ (Pin 19) is strobing, though.

I verified that my Z84C0006PEG CPU
(https://groups.google.com/forum/#!topic/n8vem/2_SBBQ3g45g) correctly
receives the 4 MHz clock on Pin 6 using my DSO.
The CPU is also addressing the ROM via M27C801 Pin 22 (Chip Enable).

Any help is greatly appreciated.

Pictures:
Loading Image...
Loading Image...

Please tell me if I should take photos of specific sections/parts.

Werner

[Werner S]

The correct links to the images are:
Loading Image...&sa=D&sntz=1&usg=AFQjCNG6yxa9dxxyF_NrAOiGJGiBfGSW2g>
Loading Image... <http://www.theoretic.de/47.jpg>

Is it not possible to edit a message over here?

[oscarv]

Werner,

Nice! A bug hunt! The board sure looks good, so...

Post by Werner S
After triple checking everything (e.g. successfully continuity testing the
whole board) I narrowed it down to the Z80 /IORQ line (Pin 20) not
strobing. /MREQ (Pin 19) is strobing, though.

If you see no action on IOREQ but MREQ is alive, it sounds like the Z80 is
not actually finding and executing the boot code - after all, if its hits
an IN or OUT instruction IOREQ moves low for sure unless the Z80 is faulty
(not likely) or somehow there's a short from IOREQ to ground (but you
checked).

So I would take a guess that the Z80 is up and running but is not reading
the ROM correctly.
Because the ROM CE does go low you would think it's not a problem with the
IO/memory management logic.

First ideas then: are the jumpers set right? And is the EPROM programmed
OK, can you read it back & verify in the eprom progammer?

Regards,

Oscar

[p***@public.gmane.org]

Hi Werner,

Oscar gave a good idea - if you have a multimeter with frequency counting mode,
connect it to /MREQ and /IOREQ lines, the signal there should be with 2x-10h
lower frequency than the CPU clock. Please check also the HALT signal, just to
be sure the CPU is still executing "something" and is not halted. When the
system boots, it looks for the UART and if the CPU can't read/write the UART
registers, it halts, so this can be a cheap check whether the clock/CPU/EPROM/UART
are properly working.

Regarding the missing console - please make sure you have CPU @ UART clocks
working, and the UART clock is with the right frequency (1.8432 MHz). Double
check also the serial speed of your PC, just to make sure it's the same as the
SBC (I do this mistake from time to time).

Please drop us a line what happens, so we can try to help more.

Regards,
picmaster

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[Ants Pants]

Post by p***@public.gmane.org
Hi Werner,

this may sound liek a no brainer but i know i had issues in this
department, check your oscillators and make sure they are giving you the
desired frequencies, by way of logic probe of oscilliscope, make sure you
are getting the 1.8432 Mhz on the CLK pin of the UART, another thing i know
had never been an issue on most users SBC is the scratch pad (address 0x6F)
of the UART, maby someone can correct me im im wrong, but the program does
a write to the scratch pad of the UART and a readback and then decideds if
it exists in hardware or not before it initalizes it, i had issue with some
very similar hardware where (using the same UART) and same code used before
on a SBC, writing to the scratch pad to verify hardware existance came back
flase and my program faulted, i got around this by just setting up the UART
without the program working out if it was there or not (i most definately
was there i could see it!! haha) and writing direct to the write register
of the UART (address 0x68), maby you could write a simple program that sets
up the UARt to your desired Baud rate and then write a character and then
delay in a loop, burn it to the UVEPROM and test it in system, the SBC
hardware is very simple and upon a reset the hardware is all there and
setup to use the UART and software stack in the higher 32k of memory. oh
and make sure you have the jumpers setup so you dont need the IREQ signal
on the UART interrupting the Z80.. just for now. to verify you have the
UART in a working state. just my thoughts.. eliminate as much of the other
hardware as possible to just check the UART.. good luck

[oscarv]

Hi,

I think in this case the problem may be much more basic than the UART block
not working.

My reasoning:

- IF you are sure there is no activity at all on IOREQ (not even a
single burst of IOREQ going low), but there IS a regular MREQ going on that
indicates the Z80 is running,
- AND you assume the Z80 CPU is undamaged (theoretically, its IOREQ pin
could be dead),
- AND you assume the IOREQ pin is not shorted to VCC on the board,
- THEN it means the CPU *is *executing *something *but *not executing *any
OUT or IN instructions after booting.


By extension, that means that the ROM is not being read correctly. Because
the boot code is a jump to $100 and then immediately a bunch of OUTs and
INs to send "RomWBW" to the serial port, meaning IOREQ starts flipping low
for a at least a brief series of instruction cycles.

What I mean: even if the UART is completely malfunctioning, you'd still see
IOREQ going low. So the UART is not what you should investigate. No IOREQ
means not executing the boot code, irrespective of whether the UART is
working or not.

So if the above assumptions are true, then reading code from ROM is your
problem, not anything with the UART.
And if the CE on the ROM is going low, it means enabling the ROM is not the
problem either. So it's either

- the contents of the ROM are not good, or
- the higher address pins on the ROM are not all 0 (that would cause the
wrong part of the ROM to be put in view of the CPU so boot code is not
run), or
- something garbles the data bus so the ROM's contents do not reach to
Z80, or
- the R/W signals do not reach the ROM.



One important caveat: if IOREQ goes low a couple times very briefly and
then no more (you could overlook that one-off burst of IOREQs) it may mean
that RAM is the problem. Because after printing "RomWBW" to the UART, the
next thing that happens is copying ROM code to RAM, and running then
proceeds from RAM. Soon after the jump to RAM, the CPU continuously starts
polling the UART for keypresses so you see constant IOREQs being made. Even
if the UART is fried. So still no need to investigate the UART.

I hope that reasoning is watertight... check points then are:
- jumpers set OK for this EPROM type?
- higher addres lines on EPROM all stay low? Because the boot code is at
the bottom of the EPROM
- does R/W signal make it to the EPROM?
- verify EPROM in EPROM burner to ensure it's the right code in there, and
it is still a working IC.

Regards,

Oscar.

[p***@public.gmane.org]

I agree with these suggestions. In the cases when a scope is out of budget to
analyze such issues, one can use a very low frequency RC-oscillator that can
clock the CPU, and to mount 2 LEDs (with resistors) to monitor the IOREQ/MREQ
lines visually. That works like a charm, just make sure you consume the minimal
needed current to blink the LEDs and not disrupt the CPU pins' normal functions
(say, <= 1mA).

Regards,
picmaster

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[Werner S]

Thank you all very much for taking the time to respond and help me fix my
board.

Let me say first that equipment-wise I have a Fluke 87 V Multimeter and a
Rigol DS1102E Digital Oscilloscope at home.


*Jumpers*

As can be seen in the picture, K1-K12 are in their default positions, i.e.
Jumper-setting 1-2. JP1 and JP2 are both not installed.

*Oscillators*

I verified both UART & CPU clock frequencies using my oscilloscope. I'm
getting the CPU clock frequency on Pin 6 of the Z80 and the UART clock
frequency on Pin 16 of the 16550.

*CPU signals*

/HALT (Pin 18) is always HIGH, so the CPU is not halted.
/RESET (Pin 26) is always high. Only as long as I keep the reset button
pushed, /RESET goes low.
/IORQ (Pin 20) is not shorted to VCC on the board.

*EPROM*

I'm using the pre-programmed EPROM that Andrew sent me because I don't have
an EPROM programmer myself. Using a breadboard and my DMM I verified the
first 8 Bytes of the EPROM to be identical to the N8VEM firmware (
http://n8vem-sbc.pbwiki.com/f/ROMIMAGE.zip). I am still waiting for my
Arduino Mega 2560R3 to read out the whole EPROM.
After a reset, EPROM address lines 15-19 stay low and 0-14 are strobing.


I agree with Oscar's reasoning: No /IOREQ means not executing the boot
code, irrespective of whether the UART is working or not. Reading code from
ROM probably is my problem and not the UART.

I don't think I overlooked any one-off bursts of /IOREQs. Using the trigger
on my oscilloscope I do not see a single negative slope after pressing the
reset button.

What can I do next?


Thanks,

Werner

[Werner S]

I just wrote a small program for my Arduino UNO that dumps the beginning of
the EPROM to the serial monitor.

You can see the result in this picture:
Loading Image...
Left: hex view of original N8VEM ROM image (
http://n8vem-sbc.pbwiki.com/f/ROMIMAGE.zip).
Right: output from Arduino code that shows the first 51 bytes of my EPROM.

You can see that the contents are not identical. My first few bytes look
very similar to the contents of memory address 0x100 on the original ROM
image.

What do you think? Is my EPROM bad or did Andrew burn my EPROM with a
different ROM image that is also OK?

[Andrew Lynch]

Hi Werner! Thanks! All of the SBC V2 pre-programmed EPROMs are the
original Mar 2008 ROMIMAGE.BIN file. It is only enough to get you started.
If you see differences between your ROM and the ROMIMAGE.BIN file then
almost certainly your EPROM was damaged. Maybe in transit or static or who
knows what else.


All the EPROMs I program are ID checked, blank checked, programmed, and
verified to be correct against the ROMIMAGE.BIN file. I suspect maybe your
EPROM got put through an X-Ray machine enroute to Germany? Maybe static? I
don't know but it sounds like your ROM is bad.



You'll need a new ROM or erase that one and try again. I suggest getting a
low cost programmer and using a 29F040 Flash memory since it also supports
in circuit reprogramming. I recommend all builders to get a programmer
since you are going to need one sooner or later any way. Thanks and have a
nice day!

Andrew Lynch







From: n8vem-/***@public.gmane.org [mailto:n8vem-/***@public.gmane.org] On Behalf Of
Werner S
Sent: Saturday, December 14, 2013 11:18 AM
To: n8vem-/***@public.gmane.org
Subject: [N8VEM: 16690] Re: New N8VEM not running - please help!



I just wrote a small program for my Arduino UNO that dumps the beginning of
the EPROM to the serial monitor.

You can see the result in this picture:
http://www.theoretic.de/comparison.png
Left: hex view of original N8VEM ROM image
(http://n8vem-sbc.pbwiki.com/f/ROMIMAGE.zip).
Right: output from Arduino code that shows the first 51 bytes of my EPROM.

You can see that the contents are not identical. My first few bytes look
very similar to the contents of memory address 0x100 on the original ROM
image.

What do you think? Is my EPROM bad or did Andrew burn my EPROM with a
different ROM image that is also OK?
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[Werner S]

Investigating a bit further, I now think that my EPROM is good after all.
It just does not contain the ROM image that I expected.

Looking at the Software and ROM images website
(http://n8vem-sbc.pbworks.com/w/page/4200935/Software-and-ROM-Images) I
expected one of the files N8VEM_SW.003.zip or ROMIMAGE.zip (both 23 May
2008)
to be pre-programmed on my EPROM because it says in the description "this
version on preprogrammed EPROMs (by Andrew Lynch)".

However, it seems that the ROM image ROMIMAGE-RC1+(2).BIN
(http://n8vem-sbc.pbworks.com/w/file/4201372/ROMIMAGE-RC1%2B%282%29.BIN )
was burnt on my EPROM. At least the first 64 Bytes are identical. See
Loading Image... (I will read out and compare the
whole EPROM next week when my Arduino Mega arrives which has more digital
pins than my Arduino Uno).

Andrew, can you confirm this?

Thanks, Werner

[Andrew Lynch]

Thanks Werner! Yes, that sounds right. One of these days we need to get an
updated "default" ROMIMAGE.BIN. We are using one that is about five years
old. There have been about three or four attempts to make a new default but
no luck so far.



Thanks and have a nice day!

Andrew Lynch



From: n8vem-/***@public.gmane.org [mailto:n8vem-/***@public.gmane.org] On Behalf Of
Werner S
Sent: Sunday, December 15, 2013 5:25 AM
To: n8vem-/***@public.gmane.org
Subject: Re: [N8VEM: 16712] Re: New N8VEM not running - please help!



Investigating a bit further, I now think that my EPROM is good after all. It
just does not contain the ROM image that I expected.

Looking at the Software and ROM images website
(http://n8vem-sbc.pbworks.com/w/page/4200935/Software-and-ROM-Images) I
expected one of the files N8VEM_SW.003.zip or ROMIMAGE.zip (both 23 May
2008)
to be pre-programmed on my EPROM because it says in the description "this
version on preprogrammed EPROMs (by Andrew Lynch)".

However, it seems that the ROM image ROMIMAGE-RC1+(2).BIN
(http://n8vem-sbc.pbworks.com/w/file/4201372/ROMIMAGE-RC1%2B%282%29.BIN )
was burnt on my EPROM. At least the first 64 Bytes are identical. See
http://www.theoretic.de/comparison2.png (I will read out and compare the
whole EPROM next week when my Arduino Mega arrives which has more digital
pins than my Arduino Uno).

Andrew, can you confirm this?

Thanks, Werner
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[Werner S]

Andrew, is it possible that you attach the ROM image file you use for the
pre-programmed EPROMs here?

I noticed differences to ROMIMAGE-RC1+(2).BIN - the file I suspected that
you use for pre-programming.

I want to see if my ROM is OK and 100% bit-identical to the ROM image file
you used.

Thank you!

[Borut]

Werner,

My guess is that rom is ok.
I would suggest you check how your serial port is connected. Iirc there is not enough to connect rx, tx and gnd but you also need to do something with handshake lines.
I usually loop them back (rts to cts amd dtr to dsr)
Then you have to set your terminal emulator to no handshake.

Bo/

[Andrew Lynch]

Hi



I am still using the original N8VEM SBC ROM BIOS software distribution.



It can be found here and includes the full source code.



http://n8vem-sbc.pbworks.com/w/file/4201303/N8VEM_SW.003.zip



Originally the plan was to make a replacement default SBC ROM BIOS image but
I don't think it ever really came to exist.



There are *many* ROM images to choose from. Choosing which one is a highly
subjective decision.



I pre-program an EPROM for some builders to get started but it is not
intended as a permanent solution. I do not want it to be a permanent
solution!



Basically it is just enough to get started and verify the SBC works. Then
as soon as possible make a new ROM BIOS for your personal needs.



I try to encourage any and all new builders to get a programmer as soon as
possible. They are indispensable tools for home brew computer hobbyists.



Then they can create their own EPROM or Flash (29C040) with a custom ROM
BIOS image like the excellent RomWBW or one of the many others available.



Ultimately the choice of ROM BIOS image is unique custom to the builders
preferences and hardware configuration.



Probably the "general solution" to the issue is to build your own custom ROM
BIOS image. I suggest the RomWBW as a great starting point.



I hope this helps! Thanks and have a nice day!

Andrew Lynch





From: n8vem-/***@public.gmane.org [mailto:n8vem-/***@public.gmane.org] On Behalf Of
Werner S
Sent: Sunday, December 15, 2013 4:43 PM
To: n8vem-/***@public.gmane.org
Subject: Re: [N8VEM: 16724] Re: New N8VEM not running - please help!



Andrew, is it possible that you attach the ROM image file you use for the
pre-programmed EPROMs here?

I noticed differences to ROMIMAGE-RC1+(2).BIN - the file I suspected that
you use for pre-programming.

I want to see if my ROM is OK and 100% bit-identical to the ROM image file
you used.

Thank you!
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[oscarv]

Andrew,

Should the RomWBW not be provided as the default eprom image? It's so far
ahead of the 2008 image that it is a must-have anyway.
Even better would the the default SBC RomWBW image with an application-boot
program in the rom disk for the PPIDE version.

Regards,

Oscar.

[Werner S]

*IT WORKS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*

I had to change the serial bitrate to 9600 bps for the serial connection to
function - opposed to the 38400 bps suggested in the "Building the N8VEM
for the Total Beginner v1.1.docx" guide. Why is that?

I was able to read out my complete EPROM using my newly-arrived Arduino
Mega. Here is it:
http://www.theoretic.de/20131218 EPROM Werner.bin.txt
I have no idea what ROM image that corresponds to. Anybody else have a
clue? Andrew?
Is there a list of commands somewhere?

*Thank you all for your tips and suggestions!*

My next step will be buying a programming device and suitable flash EEPROMs.
Regarding the burner, I cannot decide between Batronix BX40 Bagero II and

Willem True USB PRO GQ-4X, but I will create a new thread for this.

[Vince Mulhollon]

Post by Werner S
Regarding the burner, I cannot decide between Batronix BX40 Bagero II and
Willem True USB PRO GQ-4X, but I will create a new thread for this.

I have that Willem model, and it works fine although only under legacy
windows, so I have to reboot into windows every time I burn an eeprom.
Very annoying. I'll eventually get motivated enough to get it running
under WINE or in a virtualbox. Its the only "real app" I use on windows
anymore. Windows feels like about halfway in between linux and cp/m anyway
so I guess its not so inappropriate. The Willem is exceedingly easy to
use, reliably does exactly what it claims to, and low price. Other than
the "only works on legacy operating system" thing I have not discovered any
problem yet. I also do a lot of non-N8VEM things with the Willem like burn
serial eeproms for propellers and FPGAs and some non-n8vem retro projects;
it simply "just works". Its always very boring and predictable, exactly as
a good tool should behave.

I very seriously considered the Batronix, it looks nice and works under my
computers OS without rebooting, but costs about 3 times as much (for me)
and the shipping from .de to USA is about half the entire cost of the
Willem.

I checked the mcumall and batronix and as of this morning it costs around
$50 to send a little paperback book sized package between USA and Germany,
either direction. I am completely mystified how I can buy five things on
DX or ebay shipped direct from mainland China both the product and the
shipping included for the same cost as just the shipping between .us and
.de. Perhaps all shipping traffic between our countries has a shipping hub
on the moon or the planet mars rather than mere airmail like the Chinese
use, or perhaps all traffic between .us and .de is delivered by
transcontinental amazon helicopter drones, or individually delivered by
amphibious armored cars or something.

[p***@public.gmane.org]

I have a GQ-4X and it works fine under Window 7 x64 and I believe that Windows 8 drivers are available as well. Has burned & read several 2k - 1m EEPROM flawlessly.

[AG5AT]

I have an old parallel port Willem that I used to use. I found a set of
odds-and-ends drivers that make it work on Windows 7 64-bit somewhere in a
gamer site.

But on the GQ-4X. I bought one from mcumall. It isn't inexpensive. But it
works reliably and has done all of the chips that I use for N8VEM projects.

Aug
In Arkansas

Post by Werner S
*IT WORKS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*
I had to change the serial bitrate to 9600 bps for the serial connection
to function - opposed to the 38400 bps suggested in the "Building the N8VEM
for the Total Beginner v1.1.docx" guide. Why is that?
I was able to read out my complete EPROM using my newly-arrived Arduino
http://www.theoretic.de/20131218 EPROM Werner.bin.txt
I have no idea what ROM image that corresponds to. Anybody else have a
clue? Andrew?
Is there a list of commands somewhere?
*Thank you all for your tips and suggestions!*
My next step will be buying a programming device and suitable flash EEPROMs.
Regarding the burner, I cannot decide between Batronix BX40 Bagero II and
Willem True USB PRO GQ-4X, but I will create a new thread for this.

[AG5AT]

The reason you needed 9600 is that the EPROM image you are using is very
old and they were set for 9600. When you can put the newest RomWBW on it.
That will be 38k.

Aug
In Arkansas

Post by Werner S
*IT WORKS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*
I had to change the serial bitrate to 9600 bps for the serial connection
to function - opposed to the 38400 bps suggested in the "Building the N8VEM
for the Total Beginner v1.1.docx" guide. Why is that?
I was able to read out my complete EPROM using my newly-arrived Arduino
http://www.theoretic.de/20131218 EPROM Werner.bin.txt
I have no idea what ROM image that corresponds to. Anybody else have a
clue? Andrew?
Is there a list of commands somewhere?
*Thank you all for your tips and suggestions!*
My next step will be buying a programming device and suitable flash EEPROMs.
Regarding the burner, I cannot decide between Batronix BX40 Bagero II and
Willem True USB PRO GQ-4X, but I will create a new thread for this.

[oscarv]

Werner,

Congratulations! Enjoy the time warp back to the early 80s :)

I can really recommend adding RomWBW and the $5 PPIDE miniboard + CF
adapter/CF card. The moment you add that to the N8VEM, exchanging software
with your PC becomes much easier; plus you have basically infinite storage.
That transforms what the N8VEM really does for you. See my demodisk image
for the PPIDE here (link<http://obsolescence.wix.com/obsolescence#!n8vemimage/c1v04>
).

By the way - it really seems to me that the most frequent problems with
getting the N8VEM to work revolve around (a) forgetting about the battery -
I had that too, and (b) trouble with the baud rate and shorting RTS/CTS,
DTR/DSR.


Regards,

Oscar.

[Max Scane]

Hi Werner,

That is a pretty old rom image you have. Try looking in the F: drive for more files.

You should update to a more modern rom image when you can.

Regards,

Max

Sent from my iPad

Post by Werner S
IT WORKS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I had to change the serial bitrate to 9600 bps for the serial connection to function - opposed to the 38400 bps suggested in the "Building the N8VEM for the Total Beginner v1.1.docx" guide. Why is that?
http://www.theoretic.de/20131218 EPROM Werner.bin.txt
I have no idea what ROM image that corresponds to. Anybody else have a clue? Andrew?
Is there a list of commands somewhere?
Thank you all for your tips and suggestions!
My next step will be buying a programming device and suitable flash EEPROMs.
Regarding the burner, I cannot decide between Batronix BX40 Bagero II and
Willem True USB PRO GQ-4X, but I will create a new thread for this.
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<20131218 N8VEM Putty 9600bps.png>
<20131218 N8VEM HyperTerminal.png>

[oscarv]

Werner,

What a cool way to check an EPROM... so I think if the first 8 bytes are
OK, that makes it safe to assume it's burned as it should be.

Post by Werner S
After a reset, EPROM address lines 15-19 stay low and 0-14 are strobing.

So, within reason you can assume that the bank select mechanism is not the
problem - the ROM is accessed in the first 32K which is how it should be.

What can I do next?
CE was working right, is OE (I think pin 24, next to CE) also going low?
That is one thing to check.

If OE is also working as it should, it gets more intriguing. Because the
EPROM works and is programmed, the bank select is set as it should be,
hmm... unlikely but a short to VCC or GND on the data bus?

Is the CE on the RAM active? If at the same time as the CE on the ROM
that's not good of course. And is the battery circuit OK - i.e., is the
battery installed and pin 6 on the DS1210 is sending through what pin 5
receives?

Regards,

Oscar.

Post by Werner S
Thanks,
Werner

[Werner S]

Thanks again, Oscar!

*SRAM* Pin 22 (/CE) is always low, Pin 24 (/OE) is strobing.
*DS1210* Pin 5 (/CE) is strobing, Pin 6 (/CEO) is always low.

I don't have a battery installed on BT1 because I thought I don't
necessarily need one. Is this my problem? What battery exactly is needed?

[Borut]

I had a similar problem on a zeta without battery installed.
To eliminate this possibility connect backup power to vcc (i don;t know
how) or
pull out the ds1210 and put in two wires connecting pins 1 and 8 (vcc for
ram)
AND 5 and 6 (!cs for ram).

Borut

Post by Werner S
Thanks again, Oscar!
*SRAM* Pin 22 (/CE) is always low, Pin 24 (/OE) is strobing.
*DS1210* Pin 5 (/CE) is strobing, Pin 6 (/CEO) is always low.
I don't have a battery installed on BT1 because I thought I don't
necessarily need one. Is this my problem? What battery exactly is needed?

[Vince Mulhollon]

Post by Werner S
*SRAM* Pin 22 (/CE) is always low, Pin 24 (/OE) is strobing.
*DS1210* Pin 5 (/CE) is strobing, Pin 6 (/CEO) is always low.
I don't have a battery installed on BT1 because I thought I don't
necessarily need one. Is this my problem? What battery exactly is needed?

Yes a battery is required. I'm pretty sure this will get you (eventually)
to a DS1210 datasheet.

http://www.maximintegrated.com/pst/run.mvp?q=DS1210%E2%80%8E

Somewhere around page two, the fourth function of the DS1210. I'd cut and
paste but its not working (computers certainly are getting harder to use
over time!)

Anyway the short version is without at least 2V on the battery leads,
writes are blocked even with perfectly good Vcc on the theoretical idea
that being able to make unprotected writes is a bad idea. On a totally
different topic I have a different DS1210 backed up system which has off
board two AA lithium cells which should last a very long time. Anyway more
than 2V and less than 5V should be all good. I would have to think for a
bit what would happen if you shorted the battery connector (with no battery
installed) to Vcc. Maybe burn something out maybe it works. Maybe my
first try would be a 100K resistor instead of a short ckt LOL.

There is an explanation in the datasheet explaining either the failure mode
and/or how to write software to detect / work around it. It boils down to
do a read cycle, write something, then reads will fail to verify.

I donno if its even theoretically possible in the architecture to detect
dead battery at boot time. I think would manifest as something like a
memory test failure.

An excellent architectural / design issue is in a system with a DS1210 how
do you detect the difference between a boot time memory test failure and a
dead backup battery. Donno if at the hardware level its possible.
Additional circuitry might make it possible (an high impedance opamp
comparator vs a resistor divider network on VCC giving about 2.5 volts?)
Another interesting ideal might be a XOR watching the write enable going
into the DS1210 and out and if they ever disagree (aka the battery is dead)
then a flipflop could set and a memory test failure could look at that
flipflop ... somehow.... Maybe the simplest is a big bright RED led on the
output of the comparator and a printed legend something like "red light
indicates dead backup battery; won't work till replaced". A lot of the
hardware constraints boil down to the traditional trying to fit 10 sq
inches of components on a 9 sq inch board or whatever.

Or the TLDR, all writes to SRAM will fail till a battery is connected, and
this is not likely to work well.

There may, or may not, be other problems, so continued failure after
applying backup voltage does not necessarily prove further troubleshooting
should be done without backup voltage.

I think you're extremely close to a working system. Happy Holidays

[oscarv]

Werner,

*SRAM* Pin 22 (/CE) is always low, Pin 24 (/OE) is strobing.

Post by Werner S
*DS1210* Pin 5 (/CE) is strobing, Pin 6 (/CEO) is always low.
I don't have a battery installed on BT1 because I thought I don't
necessarily need one. Is this my problem? What battery exactly is needed?

Yeah - the battery thing again then! Your board is fine, it's just the
battery. That was what got me as well when I first booted my Zeta.

If you do not want to have the battery, you must remove the DS1210 and
short - er - I think pins 5-6 and maybe 1-8 on the DS1210 socket. Search
for a very similar conversation in this group about 2 months ago. It
contains the exact specifications of what to do if you do NOT want to use a
battery.

The DS1210 does something very weird when it has a battery low (or no
battery) problem: it blocks every second CE or something like that - it's
in that previous thread, here is the link (click)<https://groups.google.com/forum/#!searchin/n8vem/DS1210/n8vem/t52Hhe92m9U/_vWqxphs4bYJ>
.


Regards,

Oscar.

[oscarv]

Werner,

Actually, on second though, I am still mystified on how a missing battery
can interfere with the very first boot steps, where the N8VEM is running
out of ROM when sending out its first few bytes on the console. That makes
no sense... Still, *either *insert the battery *or *take out the DS1210 and
jumper 5-6 and 1-8 on its socket (I think, please double-check). Hopefully
that solves the problem.

Regards,

Oscar.

[Borut]

Oscar,

No ram -> no stack -> rts goes to nirvana.

Bo/

[Werner S]

Thank you all for your tips and suggestions.

The information from
http://permalink.gmane.org/gmane.comp.homebrew.n8vem/429 should be added to
the various guides/instructions - especially the "Building the N8VEM
Single-Board Computer for the Total Beginner" guide.

After removing the DS1210 and shorting pins 1-8 and 5-6, I can now finally
see strobes on the Z80 /IORQ line (Pin 20). My UART is also receiving chip
selects now.

Serial connection (I tried Putty and HyperTerminal Private Edition under
Windows 8) still does not work though, but I am using a USB-serial adaptor
which might also be the culprit.

[John Coffman]

Post by Werner S
Serial connection (I tried Putty and HyperTerminal Private Edition
under Windows 8) still does not work though, but I am using a
USB-serial adaptor which might also be the culprit.
-

RS-232 connections are an eternal headache. I connected a Wyse terminal
to my SBC v1 (and later v2), and had no operation. But I remembered
that this terminal is very finicky: it requires ALL modem control
signals to be asserted before it will function. A few jumpers added to
the connector on the end of my null modem cable, and I got it to work.

Best of luck to you with RS-232!

BTW: RD and TD should idle at -V
All control signals are asserted at +V

V = 3 to 10 volts, approximately. Generally 3 is enough.

--John

[Andrew Lynch]

Hi
That's a good point.

Please disregard my last email.

Thanks and have a nice day!

Andrew Lynch

-----Original Message-----
Behalf Of Borut
Sent: Saturday, December 14, 2013 4:56 PM
Subject: [N8VEM: 16699] Re: New N8VEM not running - please help!
Oscar,
No ram -> no stack -> rts goes to nirvana.
Bo/
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[John Coffman]

Werner,

You can run without a battery input to the DS1210, but BOTH battery
inputs must be grounded. Open circuit is not an option.

--John

Thanks again, Oscar!*
SRAM* Pin 22 (/CE) is always low, Pin 24 (/OE) is strobing.
*DS1210* Pin 5 (/CE) is strobing, Pin 6 (/CEO) is always low.
I don't have a battery installed on BT1 because I thought I don't
necessarily need one. Is this my problem? What battery exactly is needed?
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[John Coffman]

Werner,

Second option: remove the DS1210, short pins 1-8 and 5-6.

--John

[My previous message still stands: ground pin 2, VBAT1 input. VBAT2 is
already grounded on the circuit board. This way you don't have to pull
the chip out. Or, use the shorting option above.]

Thanks again, Oscar!*
SRAM* Pin 22 (/CE) is always low, Pin 24 (/OE) is strobing.
*DS1210* Pin 5 (/CE) is strobing, Pin 6 (/CEO) is always low.
I don't have a battery installed on BT1 because I thought I don't
necessarily need one. Is this my problem? What battery exactly is needed?
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[Werner S]

Thanks for your reply, Andrew.

I was a bit confused because my EPROM readout contains more than the 17K
ROMIMAGE.BIN from N8VEM_SW.003.zip - the first 17K are identical, however.

In the meantime I have bought myself a Batronix BX40 Bagero II programming
device and am running RomWBW 2.5.2 - great stuff!

Right now I'm studying CP/M internals and Z80 software development. Lots of
things to do and learn!

[Werner S]

Hi all!

My N8VEM SBC V2 is running fine without the backup battery (DS1210 removed,
pins 1-8 and 5-6 shorted).

Now I want to get it working _with_ the backup battery, but without success
so far.
After reinstalling the DS1210 and connecting a CR 2032 3V Lithium battery
(Pin1 +; Pin2 - , see attached picture), the RUN/HALT LED always
immediately turns red after booting up/reset.
I am measuring 3,2V on both DS1210 Pin 2 (VBAT1) and DS1302 Pin 8 (VBAT).

Any suggestions? Are the 3,2V of the CR2032 not sufficient?

Thanks,
Werner

[p***@public.gmane.org]

Hi Werner,

Simple possible issue can be wrong orientation of the IC in the socket,
left-over soldered wires on the other side of the PCB (both sound
impossible and yet it happens all the time), and finally the IC can be
damaged by static, factory-dead or just counter-feit. The DS1210 should
work with battery voltages over 2.0V, so your case looks fine (you can
measure again the voltage with an 1-3K load resistor just to be sure).

You can check several things:
1. Check power switching - DS1210 pin 1 should be VBAT or 5V depending
on whether the SBC is powered or not.
2. Check whether the CEO output follows CE input when SBC is powered.

Hope this helps. Regards,
picmaster


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[John Coffman]

Post by p***@public.gmane.org
Hi Werner,
Simple possible issue can be wrong orientation of the IC in the socket,
left-over soldered wires on the other side of the PCB (both sound
impossible and yet it happens all the time), and finally the IC can be
damaged by static, factory-dead or just counter-feit.

I agree w/ "picmaster." What you describe sounds like a dead DS1210.

--John

Post by p***@public.gmane.org
The DS1210 should
work with battery voltages over 2.0V, so your case looks fine (you can
measure again the voltage with an 1-3K load resistor just to be sure).
1. Check power switching - DS1210 pin 1 should be VBAT or 5V depending
on whether the SBC is powered or not.
2. Check whether the CEO output follows CE input when SBC is powered.
Hope this helps. Regards,
picmaster
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[Werner S]

Thank you both.

I just tried three different DS1210s (correct IC orientation) - without
success.

Power switching seems not to be working. DS1210 Pin 1 (VCCO) is either 5V
or 0V, but never VBAT.

[p***@public.gmane.org]

Hi Werner,

As far as I know, the power switching should work always, regardless of the
CE input. If all of your ICs are from the same supplier, you can try to buy
from another one. I don't have soldering experience with this IC, maybe other
guys can say how sensitive it is to static.

If you still want to preserve your SRAM contents while looking for another
DS1210 and you don't mind ugly hacks, you can mount 2x BAT42/BAT43 Schottky
diodes from pins 8 & 2 to pin 1, and bridge pins 5-6. This should work as a
temp replacement while hunting better parts.

Regards,
picmaster


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[John Coffman]

This is now sounding like a broken trace, or cold solder joint.

With the battery connected, is the VBAT1 voltage getting to pin 2 of the
socket? (check the socket, not the solder on the bottom)
Are pins 3, 4, and 7 solidly grounded? (check the socket, not the
solder on the bottom)
If pin 7 is not grounded, you will have trouble.

If the above are not correctly connected, then check for a cold solder
joint to the socket pins. Worst case is a broken trace on VBAT1.

Check out the above first. Broken traces have happened, are hard to
find, but easy to fix.

--John

Post by Werner S
Thank you both.
I just tried three different DS1210s (correct IC orientation) -
without success.
Power switching seems not to be working. DS1210 Pin 1 (VCCO) is either
5V or 0V, but never VBAT.
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[Werner S]

It's really strange, because everything is looking OK.

With the battery connected, the VBAT1 voltage is getting to pin 2 of the
socket (I checked the socket, not the solder on the bottom).

[John Coffman]

Since the board worked with the 1-8 & 5-6 jumpers, I would conclude that
you have 3 bad DS1210's.

--John

Post by Werner S
It's really strange, because everything is looking OK.
With the battery connected, the VBAT1 voltage is getting to pin 2 of
the socket (I checked the socket, not the solder on the bottom).
Pins 3, 4, and 7 are solidly grounded.
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[John Coffman]

On second thought, you may have a socket that is making contact with
your probe, but not with the DS1210 pins. I have never seen this, but
the socket is part of the logic path. I believe your jumpers were
soldered in place, so the socket is the other suspect, besides the 3
chips. The best you can do is to insert a chip, and check that the chip
pin is connected to the soldered underside of the board. This could
eliminate the socket as a suspect.

--John

Post by Werner S
It's really strange, because everything is looking OK.
With the battery connected, the VBAT1 voltage is getting to pin 2 of
the socket (I checked the socket, not the solder on the bottom).
Pins 3, 4, and 7 are solidly grounded.
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[Werner S]

All connections (& soldering) are fine.

I have built an isolated DS1210 test circuit and successfully verified
correct function of all three ICs.
In the test circuit power switching works as specified and /CEO output
follows /CE input (when not powered from battery).

With the battery connected and the DS1210 reinserted in my N8VEM, I still
get the red LED to light up. Most of the time the LED turns red immediately
after power-on/reset, sometime it turns red when I plug my USB-serial
adaptor in my computer's USB port.
I am suspecting a power issue. Could it be that the voltage output from the
USB cable I use to power my N8VEM is not sufficient?
I am measuring (in-circuit, power on) ~4,5V (sometimes less) on Pins 1
(VCCO) and 8 (VCCI). /CE seems to strobe (DMM shows 3,3V), but /CEO seems
to be permanently low.

[Tregare]

Um. I'd try a different 5V source, USB has a current limit, and it varies
depending on which port you are pulling it from. (some USB ports on
computers only allow 150ma current, some 500ma, some 1a....

Post by Werner S
All connections (& soldering) are fine.
I have built an isolated DS1210 test circuit and successfully verified
correct function of all three ICs.
In the test circuit power switching works as specified and /CEO output
follows /CE input (when not powered from battery).
With the battery connected and the DS1210 reinserted in my N8VEM, I still
get the red LED to light up. Most of the time the LED turns red immediately
after power-on/reset, sometime it turns red when I plug my USB-serial
adaptor in my computer's USB port.
I am suspecting a power issue. Could it be that the voltage output from
the USB cable I use to power my N8VEM is not sufficient?
I am measuring (in-circuit, power on) ~4,5V (sometimes less) on Pins 1
(VCCO) and 8 (VCCI). /CE seems to strobe (DMM shows 3,3V), but /CEO seems
to be permanently low.
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[John Coffman]

I wonder if the DS1210's think that at 4.5v the power is failing?

--John

Post by Tregare
Um. I'd try a different 5V source, USB has a current limit, and it
varies depending on which port you are pulling it from. (some USB
ports on computers only allow 150ma current, some 500ma, some 1a....
All connections (& soldering) are fine.
I have built an isolated DS1210 test circuit and successfully
verified correct function of all three ICs.
In the test circuit power switching works as specified and /CEO
output follows /CE input (when not powered from battery).
With the battery connected and the DS1210 reinserted in my N8VEM,
I still get the red LED to light up. Most of the time the LED
turns red immediately after power-on/reset, sometime it turns red
when I plug my USB-serial adaptor in my computer's USB port.
I am suspecting a power issue. Could it be that the voltage output
from the USB cable I use to power my N8VEM is not sufficient?
I am measuring (in-circuit, power on) ~4,5V (sometimes less) on
Pins 1 (VCCO) and 8 (VCCI). /CE seems to strobe (DMM shows 3,3V),
but /CEO seems to be permanently low.
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[Tregare]

Give the man a cigar :)

according to the datasheet...

Power fail detection occurs in the range of 4.75 volts to 4.5 volts with
the tolerance
(TOL) pin grounded. If TOL is connected to VCCO, then powerfail detection
occurs in the range of 4.5 volts to 4.25 volts.

Post by John Coffman
I wonder if the DS1210's think that at 4.5v the power is failing?
--John

Post by Tregare
Um. I'd try a different 5V source, USB has a current limit, and it
varies depending on which port you are pulling it from. (some USB
ports on computers only allow 150ma current, some 500ma, some 1a....
All connections (& soldering) are fine.
I have built an isolated DS1210 test circuit and successfully
verified correct function of all three ICs.
In the test circuit power switching works as specified and /CEO
output follows /CE input (when not powered from battery).
With the battery connected and the DS1210 reinserted in my N8VEM,
I still get the red LED to light up. Most of the time the LED
turns red immediately after power-on/reset, sometime it turns red
when I plug my USB-serial adaptor in my computer's USB port.
I am suspecting a power issue. Could it be that the voltage output
from the USB cable I use to power my N8VEM is not sufficient?
I am measuring (in-circuit, power on) ~4,5V (sometimes less) on
Pins 1 (VCCO) and 8 (VCCI). /CE seems to strobe (DMM shows 3,3V),
but /CEO seems to be permanently low.
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[p***@public.gmane.org]

Hi Tregare,

I also found this text in the datasheet, but my interpretation is that
this power fail detection is related only to the CE/CEO control, and not
the actual power switching. But in any case, your comment is a good point
to remind the actual voltage thresholds of the chip.

@Werner - do you have access to a better 5V power supply, so you can see
how the SBC behaves there?

@Everyone - guys, what's the "expected" power consumption of a completed
TTL SBC?

Regards,
picmaster


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[Werner S]

Thanks guys for your help.

Unfortunately I don't have a variable laboratory power supply.

I just powered the N8VEM via a regulated AC/DC adaptor (1A max, set to
7,5V) and a TS7805 with the following outcome:

- RUN/HALT LED always green (good)
- No serial connection possible (bad)

1. Power supply ON:

- DS1210 Pins 8 (VCCI) and 1 (VCCO): 4,4V (maybe too low?)
- DS1210 Pin 2 (VBAT1): 3,2V (good)
- DS1210 Pin 5 (/CE): 2,1V (seems to be strobing)
- DS1210 Pin 6 (/CEO): 4,4V (HIGH)

2. Power supply then turned OFF:

- DS1210 Pin 1 (VCCO): 3,2V (battery voltage, power switching working)
- DS1210 Pin 6 (/CEO): 3,2V (HIGH)


Thanks,

Werner

[Jörg Schöning]

Hallo Werner,

sind am Eingang des 7805 wirklich 7,5 Volt? Das wäre das Minimum für so
einen Spannungsregler. Hast Du am Ausgang +5 Volt? Es scheint so das der
7805 nur 4,4 Volt liefert weil er zu wenig Spannung zum regeln am Eingang
hat. Die Ausgangsspannung am AC/DC Adapter fällt bei Belastung möglicher
Weise unter 7,5 Volt. Bitte kontrolliere diese Spannungen ein mal.

Viele Grüße
Jörg

Post by Werner S
Thanks guys for your help.
Unfortunately I don't have a variable laboratory power supply.
I just powered the N8VEM via a regulated AC/DC adaptor (1A max, set to
- RUN/HALT LED always green (good)
- No serial connection possible (bad)
- DS1210 Pins 8 (VCCI) and 1 (VCCO): 4,4V (maybe too low?)
- DS1210 Pin 2 (VBAT1): 3,2V (good)
- DS1210 Pin 5 (/CE): 2,1V (seems to be strobing)
- DS1210 Pin 6 (/CEO): 4,4V (HIGH)
- DS1210 Pin 1 (VCCO): 3,2V (battery voltage, power switching working)
- DS1210 Pin 6 (/CEO): 3,2V (HIGH)
Thanks,
Werner
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[Werner S]

Thank you Jörg!

I controlled these voltages as you said and they seem ok. I tried higher
settings (e.g. 9V) on my AC/DC adaptor, but also without success. I always
measure ~5V at the 7805 output and ~4,4V on the DS1210, no matter if I use
the 7,5V setting or those above.

Werner

Post by Jörg Schöning
Hallo Werner,
sind am Eingang des 7805 wirklich 7,5 Volt? Das wäre das Minimum für so
einen Spannungsregler. Hast Du am Ausgang +5 Volt? Es scheint so das der
7805 nur 4,4 Volt liefert weil er zu wenig Spannung zum regeln am Eingang
hat. Die Ausgangsspannung am AC/DC Adapter fällt bei Belastung möglicher
Weise unter 7,5 Volt. Bitte kontrolliere diese Spannungen ein mal.
Viele Grüße
Jörg

Post by Werner S
Thanks guys for your help.
Unfortunately I don't have a variable laboratory power supply.
I just powered the N8VEM via a regulated AC/DC adaptor (1A max, set to
- RUN/HALT LED always green (good)
- No serial connection possible (bad)
- DS1210 Pins 8 (VCCI) and 1 (VCCO): 4,4V (maybe too low?)
- DS1210 Pin 2 (VBAT1): 3,2V (good)
- DS1210 Pin 5 (/CE): 2,1V (seems to be strobing)
- DS1210 Pin 6 (/CEO): 4,4V (HIGH)
- DS1210 Pin 1 (VCCO): 3,2V (battery voltage, power switching working)
- DS1210 Pin 6 (/CEO): 3,2V (HIGH)
Thanks,
Werner
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[p***@public.gmane.org]

Hi Werner,

Do you have around a 5V charger for Android phone? These typically provide
more than 500mA and can be a good replacement for lab supply for a while.

Regards,
picmaster

-------------------------------------
Mail.BG: Безплатен e-mail адрес. Най-добрите характеристики на българския пазар - 20 GB пощенска кутия, 1 GB прикрепен файл, безплатен POP3, мобилна версия, SMS известяване и други. http://mail.bg

[Werner S]

I don't see a difference using a Nexus 5 charger: ~4,4V on Pins 1&8 and no
serial connection possible...

However, when I remove both the battery and the DS1210 and then short pins
1&8 and 5&6, serial connection works immediately.

Post by p***@public.gmane.org
Hi Werner,
Do you have around a 5V charger for Android phone? These typically provide
more than 500mA and can be a good replacement for lab supply for a while.
Regards,
picmaster
-------------------------------------
Mail.BG: Áåçïëàòåí e-mail àäðåñ. Íàé-äîáðèòå õàðàêòåðèñòèêè íà áúëãàðñêèÿ
ïàçàð - 20 GB ïîùåíñêà êóòèÿ, 1 GB ïðèêðåïåí ôàéë, áåçïëàòåí POP3, ìîáèëíà
âåðñèÿ, SMS èçâåñòÿâàíå è äðóãè. http://mail.bg

[Jörg Schöning]

Hi Werner,

I do not understand. Vcci = Vcco? So 4.4 volts.
VCCI is equal to Vcc. There +5 volts must have. Are at all TTL devices +5
volts? GND Pin 14, 16, 20?

best regards,
joerg

Post by Werner S
I don't see a difference using a Nexus 5 charger: ~4,4V on Pins 1&8 and no
serial connection possible...
However, when I remove both the battery and the DS1210 and then short pins
1&8 and 5&6, serial connection works immediately.

Post by p***@public.gmane.org
Hi Werner,
Do you have around a 5V charger for Android phone? These typically provide
more than 500mA and can be a good replacement for lab supply for a while.
Regards,
picmaster
-------------------------------------
Mail.BG: Áåçïëàòåí e-mail àäðåñ. Íàé-äîáðèòå õàðàêòåðèñòèêè íà áúëãàðñêèÿ
ïàçàð - 20 GB ïîùåíñêà êóòèÿ, 1 GB ïðèêðåïåí ôàéë, áåçïëàòåí POP3, ìîáèëíà
âåðñèÿ, SMS èçâåñòÿâàíå è äðóãè. http://mail.bg
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[Werner S]

Hi Jörg!

What I mean is the following:

- When I measure the voltages with the N8VEM powered up and all ICs
inserted, I get the 4,4V on all ICs.
- When all ICs are removed, I am measuring ~5V on all IC sockets.

Thanks!

Post by p***@public.gmane.org
Hi Werner,
I do not understand. Vcci = Vcco? So 4.4 volts.
VCCI is equal to Vcc. There +5 volts must have. Are at all TTL devices +5
volts? GND Pin 14, 16, 20?
best regards,
joerg

Post by Werner S
I don't see a difference using a Nexus 5 charger: ~4,4V on Pins 1&8 and
no serial connection possible...
However, when I remove both the battery and the DS1210 and then short
pins 1&8 and 5&6, serial connection works immediately.

Post by p***@public.gmane.org
Hi Werner,
Do you have around a 5V charger for Android phone? These typically provide
more than 500mA and can be a good replacement for lab supply for a while.
Regards,
picmaster
-------------------------------------
Mail.BG: БезплатеМ e-mail аЎрес. Най-ЎПбрОте характерОстОкО Ма
българскОя пазар - 20 GB пПщеМска кутОя, 1 GB прОкрепеМ файл, безплатеМ
POP3, ЌПбОлМа версОя, SMS ОзвестяваМе О ЎругО. http://mail.bg
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[Jörg Schöning]

Hi Werner,

Ok.
And you use the Nexus Charger as shown photo?
This is a switching Powersupply. Maybe the kabels are too thin.
Switching Powersupplys need more kabel diameter.

best regards,
joerg

Post by Werner S
Hi Jörg!
- When I measure the voltages with the N8VEM powered up and all ICs
inserted, I get the 4,4V on all ICs.
- When all ICs are removed, I am measuring ~5V on all IC sockets.
Thanks!

Post by p***@public.gmane.org
Hi Werner,
I do not understand. Vcci = Vcco? So 4.4 volts.
VCCI is equal to Vcc. There +5 volts must have. Are at all TTL devices +5
volts? GND Pin 14, 16, 20?
best regards,
joerg

Post by Werner S
I don't see a difference using a Nexus 5 charger: ~4,4V on Pins 1&8 and
no serial connection possible...
However, when I remove both the battery and the DS1210 and then short
pins 1&8 and 5&6, serial connection works immediately.

Post by p***@public.gmane.org
Hi Werner,
Do you have around a 5V charger for Android phone? These typically provide
more than 500mA and can be a good replacement for lab supply for a while.
Regards,
picmaster
-------------------------------------
Mail.BG: БезплатеМ e-mail аЎрес. Най-ЎПбрОте характерОстОкО Ма
българскОя пазар - 20 GB пПщеМска кутОя, 1 GB прОкрепеМ файл, безплатеМ
POP3, ЌПбОлМа версОя, SMS ОзвестяваМе О ЎругО. http://mail.bg
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