[N8VEM: 20068] N8 "Red Version" video output

Discussion:

Gary Kaufman

2015-09-03 03:23:19 UTC

I've just built up one of the last batch of N8 "red" boards. It seems to
be working nicely with the RomWBW v2.7.1 thru the serial port. I don't
seem to get any output from the composite video. I'm using the FMS6141
Video Amplifer and have omitted the 2N304. There seems to be oscillation
from the 10.7mhz xtal and activity on the RAM address/data lines but no
video output.

Thanks for any hints!

- Gary

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Wayne Warthen

2015-09-04 04:26:34 UTC

Permalink

Hi Gary,

I just tried video on my N8 running v2.7.1. It "sort of" works. The VDU
chip in the N8 is pretty slow compared to the CPU. You may notice that the
config for the N8 uses the maximum possible I/O wait states to try and
compensate for this. However, in a recent release of RomWBW I made it go
faster by disabling RAM refresh cycles which were on by default. When I
did that, I think I made the system too fast for the VDU again. I will see
if I can add a bit more delay in the VDU driver delay loops to compensate.
Will work on this over the weekend.

With all that said, note that my video is working. I just get somewhat
garbled text, but there is a valid cursor that moves as I type. There is a
good chance that you are having a different problem.

Thanks,

Wayne

Post by Gary Kaufman
I've just built up one of the last batch of N8 "red" boards. It seems to
be working nicely with the RomWBW v2.7.1 thru the serial port. I don't
seem to get any output from the composite video. I'm using the FMS6141
Video Amplifer and have omitted the 2N304. There seems to be oscillation
from the 10.7mhz xtal and activity on the RAM address/data lines but no
video output.
Thanks for any hints!
- Gary

Gary Kaufman

2015-09-05 21:31:38 UTC

Permalink

Wayne -

Thanks for helping - I do think you're correct that I'm having another
issue.

I'm having two problems with my N8. The first is the lack of any video
output from the 9918A - I've tried swapping video ram, the 9918A etc
without any success. I'll try and scope things out a bit later this
weekend.

I'm also noticing that the N8 is only finding 512K of ram, even though both
SRAM's are installed.

- Gary

Post by Wayne Warthen
Hi Gary,
I just tried video on my N8 running v2.7.1. It "sort of" works. The VDU
chip in the N8 is pretty slow compared to the CPU. You may notice that the
config for the N8 uses the maximum possible I/O wait states to try and
compensate for this. However, in a recent release of RomWBW I made it go
faster by disabling RAM refresh cycles which were on by default. When I
did that, I think I made the system too fast for the VDU again. I will see
if I can add a bit more delay in the VDU driver delay loops to compensate.
Will work on this over the weekend.
With all that said, note that my video is working. I just get somewhat
garbled text, but there is a valid cursor that moves as I type. There is a
good chance that you are having a different problem.
Thanks,
Wayne

Wayne Warthen

2015-09-05 23:13:42 UTC

Permalink

Hi Gary,

RomWBW does NOT detect the amount of RAM in your system. It assumes 512K
because that is prettysafe. You can change the config file to reflect
1024K of RAM. Of course, that does require building a new ROM, but that is
not hard. See Build.txt in the Doc folder.

I just did a bit of testing on my N8 and I definitely see where the system
is going a bit too fast for the video chip. If you are able to modify the
n8_2312.asm config file and do a new build, you can try making the
following change. This will cause the CPU to run at half speed.

Z180_CLKDIV .EQU 1 ; 0=OSC/2, 1=OSC/1

to:

Z180_CLKDIV .EQU 0 ; 0=OSC/2, 1=OSC/1

After this, build a new ROM image and try it. Note that you will need to
change the serial port speed on your terminal emulator from 38,400 to
19,200 baud. Running the CPU at half speed will also cause the serial port
baud rate to run at half speed.

Thanks,

Wayne

Post by Gary Kaufman
Wayne -
Thanks for helping - I do think you're correct that I'm having another
issue.
I'm having two problems with my N8. The first is the lack of any video
output from the 9918A - I've tried swapping video ram, the 9918A etc
without any success. I'll try and scope things out a bit later this
weekend.
I'm also noticing that the N8 is only finding 512K of ram, even though
both SRAM's are installed.
- Gary

Post by Gary Kaufman
I've just built up one of the last batch of N8 "red" boards. It seems
to be working nicely with the RomWBW v2.7.1 thru the serial port. I don't
seem to get any output from the composite video. I'm using the FMS6141
Video Amplifer and have omitted the 2N304. There seems to be oscillation
from the 10.7mhz xtal and activity on the RAM address/data lines but no
video output.
Thanks for any hints!
- Gary

Gary Kaufman

2015-09-10 12:59:54 UTC

Permalink

Wayne -

Thanks, I'll give it a try once a few 27C801's I have on order arrive from
China.

- Gary

Post by Wayne Warthen
Hi Gary,
RomWBW does NOT detect the amount of RAM in your system. It assumes 512K
because that is prettysafe. You can change the config file to reflect
1024K of RAM. Of course, that does require building a new ROM, but that is
not hard. See Build.txt in the Doc folder.
I just did a bit of testing on my N8 and I definitely see where the system
is going a bit too fast for the video chip. If you are able to modify the
n8_2312.asm config file and do a new build, you can try making the
following change. This will cause the CPU to run at half speed.
Z180_CLKDIV .EQU 1 ; 0=OSC/2, 1=OSC/1
Z180_CLKDIV .EQU 0 ; 0=OSC/2, 1=OSC/1
After this, build a new ROM image and try it. Note that you will need to
change the serial port speed on your terminal emulator from 38,400 to
19,200 baud. Running the CPU at half speed will also cause the serial port
baud rate to run at half speed.
Thanks,
Wayne

Post by Wayne Warthen
Hi Gary,
I just tried video on my N8 running v2.7.1. It "sort of" works. The
VDU chip in the N8 is pretty slow compared to the CPU. You may notice that
the config for the N8 uses the maximum possible I/O wait states to try and
compensate for this. However, in a recent release of RomWBW I made it go
faster by disabling RAM refresh cycles which were on by default. When I
did that, I think I made the system too fast for the VDU again. I will see
if I can add a bit more delay in the VDU driver delay loops to compensate.
Will work on this over the weekend.
With all that said, note that my video is working. I just get somewhat
garbled text, but there is a valid cursor that moves as I type. There is a
good chance that you are having a different problem.
Thanks,
Wayne

Post by Gary Kaufman
I've just built up one of the last batch of N8 "red" boards. It seems
to be working nicely with the RomWBW v2.7.1 thru the serial port. I don't
seem to get any output from the composite video. I'm using the FMS6141
Video Amplifer and have omitted the 2N304. There seems to be oscillation
from the 10.7mhz xtal and activity on the RAM address/data lines but no
video output.
Thanks for any hints!
- Gary