exxos's Atari, Amiga & retro forum

It’s here and booting… it did not work with the V9958 chip I had so I had to desolder a 9938 from a Rev0

Any clues as to why it wouldn't work with the V9958? Timing?

I've really not dug into it yet. I could be as simple as my 9958 chip is dead. I have no way to verify.

This board is tiny!

arkadiusz.makarenko wrote: 20 Oct 2021 10:15 This board is tiny!

Yeah. I am waiting for VDP chip and i'll make you up a board. I've reclaimed some ARM Chips hope they work. Also these boards have 288 CPLDs on them because thats what i have spare. But they should manage to work with a 144 for "Production"

I will prepare initial firmware for f722 as I have few of them just now. But for production I will downgrade it to f730, as it is few £ cheaper and usually* more available. Unless more flash and sram would be somehow useful.

* chip shortage changed that, hopefully temporarily.

Ps
Do you have gerbers for that cart pcb or dod you buy it somewhere (local)?

arkadiusz.makarenko wrote: 20 Oct 2021 12:36 I will prepare initial firmware for f722 as I have few of them just now. But for production I will downgrade it to f730, as it is few £ cheaper and usually* more available. Unless more flash and sram would be somehow useful.

* chip shortage changed that, hopefully temporarily.

Ps
Do you have gerbers for that cart pcb or dod you buy it somewhere (local)?

Ah that cart was supplied by BanjoGuyOllie.

https://www.etsy.com/uk/listing/7078448 ... ve_4&crt=1

Not expensive really.

EDIT: Also yes.. Whichever arm can do the job and is cheaper lets go with.

Cool... looking forward to this.

There are some slight differences between 9938/9958, main 3 are:

Pin 21 - V9938 uses this pin as composite video output, V9958 uses it as power supply for video DAC.
Pin 26 - V9938 can use this pin as a light pen switch input. V9958 uses it as /WAIT signal to CPU.
Pin 5/6 - Both V9938 and V9958 use this as H/CSYNC voltage levels are different.

Also pin 4,8, and 27 have been modified, see page 12 of the 9958 technical manual:

https://retrobrewcomputers.org/n8vem-pb ... asheet.pdf

Gooeyblob wrote: 20 Oct 2021 18:35 Cool... looking forward to this.

There are some slight differences between 9938/9958, main 3 are:

Pin 21 - V9938 uses this pin as composite video output, V9958 uses it as power supply for video DAC.
Pin 26 - V9938 can use this pin as a light pen switch input. V9958 uses it as /WAIT signal to CPU.
Pin 5/6 - Both V9938 and V9958 use this as H/CSYNC voltage levels are different.

Also pin 4,8, and 27 have been modified, see page 12 of the 9958 technical manual:

https://retrobrewcomputers.org/n8vem-pb ... asheet.pdf

OK i have:-

pin 21 NC. (could be the reason no output)
pin 26 is tied to VCC.

5/6 are the syncs. I am getting sync signals .. just no video.

pin 4 is NC its some kind of reset in. The manual says it will float.
pin 8 i have the CPU clock connected as an input... this may be wrong. I need to check 9938 behaviour.
pin 27 is tied to VCC.

These are branded as drop in replacements.. :/

EDIT: well that was useful. pin 8 is an output on both chips. I should remove the inline resistor and that will solve the problem.

Ok i have the 9958 working fine. I noticed i'm not doing a long enough POR either so i'll see if i can sort that in the CPLD

Adjustment of the POR time fixed my power on sometimes not working thing.