[N8VEM: 16099] SBC-V2 schematic

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

Gents,

First, hi to everyone and thanks to anyone who's efforts made this nice hobby project available.
Second, I'm building a Z80-based SBC-V2, and I think I found a small mistake on the schematic, assuming that this is the latest one: http://n8vem-sbc.pbworks.com/w/file/28766758/sbcv2%20SBC-schematic.pdf . What is the accepted way to report the issue?

P.S.: Here's a photo of my first attempt to see N8VEM SBC working: Loading Image...
The debug monitor and CPM boot messages are printed OK (taking into account that the UART clock is with wrong frequency, the SRAM & EPROM chips are smaller than required, and memory paging ICs are missing), and finally when the system tries to remap some 32K pages aroung (I suppose for disk drive access) then it hangs. Still, this is a cool progress for me.
I'm currently working on a second attempt to add all missing chips and make the system boot properly. I can show photos when it's ready.

Regards,
Nikolay

-------------------------------------

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[John Coffman]

Nikolay,

The SBC v2 had several improvements over the SBC v1, including fixes for
a couple of problems. However, it is entirely possible that obscure
problem(s) may remain.

I suggest you send your findings to Andrew, myself, or (better yet) the
list. A description of the nature of the suspected problem should
include chip locations, chip types, signal names, and pin numbers. If a
schematic would better describe the problem, I have found photos of
hand-drawn partial logic schematics to be useful.

Anyhow, if the board has issues, we all would like to know of them.

--John

Post by p***@public.gmane.org
Gents,
First, hi to everyone and thanks to anyone who's efforts made this nice hobby project available.
Second, I'm building a Z80-based SBC-V2, and I think I found a small mistake on the schematic, assuming that this is the latest one: http://n8vem-sbc.pbworks.com/w/file/28766758/sbcv2%20SBC-schematic.pdf . What is the accepted way to report the issue?
P.S.: Here's a photo of my first attempt to see N8VEM SBC working: http://s15.postimg.org/ampi0whor/20130819_170729.jpg
The debug monitor and CPM boot messages are printed OK (taking into account that the UART clock is with wrong frequency, the SRAM & EPROM chips are smaller than required, and memory paging ICs are missing), and finally when the system tries to remap some 32K pages aroung (I suppose for disk drive access) then it hangs. Still, this is a cool progress for me.
I'm currently working on a second attempt to add all missing chips and make the system boot properly. I can show photos when it's ready.
Regards,
Nikolay
-------------------------------------
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Пазарувай изгодно всеки ден на fashionsureme.bg
Нови модни марки в разпродажби всеки ден!
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[p***@public.gmane.org]

Hi John, guys,

The schematic issue is related with pin numbering and naming of 16C550 UART. In the UART specs the pins are described as "pin 21 /DISTR" and "pin 22 DISTR", and in the official SBC V2 schematic these pins are referred as the opposite polarity: "pin 21 DISTR", "pin 22 /DISTR".

In terms of schematic & layout, pin 21 is still the proper pin to receive the "/RD" signal from the CPU, so generally the boards are OK and have no issues, but still the schematic is misleading. It would be great if someone can swap the signal descriptions of pins 21 & 22 and update the published PDF.

Have a nice day,
picmaster

P.S.: Hope this helps to someone - I used EXAR ST16C550 chip for the UART, and it worked fine (it's rare to find these days good DIP UARTs).

Post by John Coffman
I suggest you send your findings to Andrew, myself, or (better yet) the
list.

-------------------------------------

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[Sergey]

My $0.02:

16550 compatible UARTs are not very hard to find (at least in US). Mouser
still has Exar ST16C550CP40-F, I am pretty sure Jameco and Unicorn
Electronics have some 16550/16C550 ICs too.

With that being said it seems that Exar is the only company that sill makes
UARTs in PDIP packages, and these are already marked as "not recommended
for new designs"... So it make sense to redesign boards for PLCC-44 chips,
using through hole sockets for easy assembly. For example mouser has 16
different 16550 compatible UARTs in PLCC-44 package, including advanced
variants (16C650, 16C750, 16C850), and only one mentioned above Exar UART
in PDIP package...

Thanks,
Sergey

Post by p***@public.gmane.org
Hi John, guys,
The schematic issue is related with pin numbering and naming of 16C550
UART. In the UART specs the pins are described as "pin 21 /DISTR" and "pin
22 DISTR", and in the official SBC V2 schematic these pins are referred as
the opposite polarity: "pin 21 DISTR", "pin 22 /DISTR".
In terms of schematic & layout, pin 21 is still the proper pin to receive
the "/RD" signal from the CPU, so generally the boards are OK and have no
issues, but still the schematic is misleading. It would be great if someone
can swap the signal descriptions of pins 21 & 22 and update the published
PDF.
Have a nice day,
picmaster
P.S.: Hope this helps to someone - I used EXAR ST16C550 chip for the UART,
and it worked fine (it's rare to find these days good DIP UARTs).
23.08.2013 â 07:07 -----

Post by John Coffman
I suggest you send your findings to Andrew, myself, or (better yet) the
list.

-------------------------------------
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