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N8-4314 with RomWBW - problems with serial [message #10322]

Sat, 29 April 2023 05:08

larryl
Messages: 4
Registered: September 2018
Location: Germany

Junior Member

Hi,

Just built a N8 based on the latest 4314 schematics
Using latest RomWBW 3.2.1

Seems to run, but I have no output via serial-0
Tried different baud rates (RomWBW say 38400 8N1 no handshake)
But this leads to nothing
Tried with other rates 9600, 14400, where I receive something, but only garbage
Activated the output to CVBS via the TMS and there I can see that RomWBW is booting

Struggled a bit with the BOM since this seems to be related to older PCB versions (2511/2312), esp the OSC for the serial
Not sure, if this needs to be 16MHz like in the BOM, or 2.4576MHz like in the schematic and in some photos I have seen in the old wiki
Tried both OSC, no joy...

Any ideas?

Thanks
Michael

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Re: N8-4314 with RomWBW - problems with serial [message #10324 is a reply to message #10322]

Mon, 01 May 2023 10:45

larryl
Messages: 4
Registered: September 2018
Location: Germany

Junior Member

Found the problem...
Just a flaky MAX232- replaced with another and now I have a stable serial output at the usual rate 38400
Seems, the crystal I was looking at, has nothing to do with the serial connection - works with. 16MHz and with 2.4576MHz
Not idea, what this OSC is for...

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Re: N8-4314 with RomWBW - problems with serial [message #10325 is a reply to message #10324]

Mon, 01 May 2023 11:41

gkaufman
Messages: 186
Registered: October 2015

Senior Member

Glad you found the problem!

Here I'm using 18.342mhz oscillator and 38,400 8/n/1 with a null modem cable. I believe the 16mhz oscillator is for the floppy circuit only.

Most of the Chinese MAX232's are flakey at best.

I did burn a RomWBW version for the TMS9918, but the 40 columns makes it fairly useless. I haven't corrected the RAM max 512K yet, I'll do that shortly.

Very nice board, the sound output is a fun feature.

- Gary

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Re: N8-4314 with RomWBW - problems with serial [message #10326 is a reply to message #10325]

Mon, 01 May 2023 15:34

larryl
Messages: 4
Registered: September 2018
Location: Germany

Junior Member

Yes, right - 40. column mode is a bit confusing...

I am using the same OSC for the CPU, and yes there is a 16MHz crystal for the Floppy.
But I was referring to the third crystal on the board, just above AY and 8255

Thought it was for the Serial, but learned that the ASCI is inside the Z180

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Re: N8-4314 with RomWBW - problems with serial [message #10327 is a reply to message #10326]

Mon, 01 May 2023 20:01

gkaufman
Messages: 186
Registered: October 2015

Senior Member

I recall that is a spare oscillator location, not sure of the purpose. I don't have it populated on my board.

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