Charles MacDonald

I recently opened up a Visicom cartridge to confirm the pin assignments. It isn't the same as a RCA Studio 2 cartridge apparently. Inside is a Toshiba TMM331AP ROM, which is pin compatible with the Signetics S6831: http://www.datasheet...-datasheet.html The cartridge to TMM331 pin connections are as follows, with cartridge pin 1 being the leftmost angled contact: Pin 1 to ROM pins 12,13 (GND and E2) Pin 2 to ROM pins 24,15 (VCC and E0) Pin 3 to ROM pin 23 (D0) Pin 4 to ROM pin 22 (D1) Pin 5 to ROM pin 21 (D2) Pin 6 to ROM pin 20 (D3) Pin 7 to ROM pin 19 (D4) Pin 8 to ROM pin 18 (D5) Pin 9 to ROM pin 17 (D6) Pin 10 to ROM pin 16 (D7) Pin 11 to ROM pin 14 (E1) Pin 12 to ROM pin 11 (A6) Pin 13 to ROM pin 10 (A5) Pin 14 to ROM pin 9 (A4) Pin 15 to ROM pin 8 (A3) Pin 16 to ROM pin 7 (A2) Pin 17 to ROM pin 6 (A1) Pin 18 to ROM pin 5 (A0) Pin 19 to ROM pin 1 (A7) Pin 20 to ROM pin 4 (A10) Pin 21 to ROM pin 3 (A9) Pin 22 to ROM pin 2 (A8) Hope this helps anybody working with these carts.

That was exactly what I needed. Interesting that the MARIA wasn't directly developed by Atari, but rather GCC. I wonder about that GCC1712 part with the 16-bit data bus - sounds intriguing!

Is there any kind of datasheet or other Atari documentation that explains the various MARIA pin functions? If not, do you know what the color delay is exactly? Thanks for all the answers!

Got a few Q's about the 7800 hardware: - Does MARIA drive A11-A15 when doing DMA? E.g. could video data be read out of ROM? - What does the DE pin (pin 9) on the MARIA chip do? Does it have any relation to the TIA DEL pin (pin 10)? - When the BIOS ROM is enabled, is it mapped to the $8000-$FFFF range? Docs say $F000-$FFFF but it looks like the output latch and A15 are all that's used. - The MARIA and TIA video busses are combined in an OR latch. Considering the TIA video registers are not accessible when 7800 mode is enabled, could meaningful video data be programmed in the TIA (say the 20-bit playfield registers) and then switch modes to have the MARIA video combined with the TIA display? - I assume the RIOT RAM is fully accessible and functions normally as expected? Or did Atari not advise 7800 programmers to use it, and it was for 2600 compatibility only? - Somebody mentioned the timer component of the RIOT loses cycles. I assume this is due to the phase 2 clock generated by MARIA getting slowed down during TIA register access?