I'm thinking about designing an expansion board to sit on top of my SXB to add some useful bits and pieces.

I've bought some 12ns 512Kx8 SRAM so at least two of those need to be added along with some decoding via an ATF1504AS.

Compact flash card modules are 5V compatible so the board could use the PIA ports and part of the user VIA to generate a full 16-bit IDE bus and control signals routed to a suitable dual pin header.

A battery backed RTC would be useful probably connected via SPI but should I bit bash off the VIA or use something like the SPI65? Can SPI65 be ported to more readily available CPLD?

More UARTs like the MAX3100 via SPI or memory mapped NXPs -- The SXB has some already decoded chip selects on its I/O page ($7fxx). The ATF1504 should have spare logic to combine any interrupt signals into a /IRQ to feed back to the 65C816.

Generating video is a pain. A microcontroller can do low resolution VGA but at 8MHz the interface would need to be serial or SPI in which case using the SPI to connect to an FTDI EVE display might be better.

What do other SXB owners think would be useful?

_________________
Andrew Jacobs
6502 & PIC Stuff - http://www.obelisk.me.uk/
Cross-Platform 6502/65C02/65816 Macro Assembler - http://www.obelisk.me.uk/dev65/
Open Source Projects - https://github.com/andrew-jacobs

Good idea on an expansion board. I've also considered adding compact flash, RTC and some other bits to my board set. Adding memory as parallel stuff makes sense and using a glue chip is a good idea to keep things small. I've also picked up some RTC chips that interface easily as parallel to the 65xx bus and there are many other UARTs that can be added the same way. If you're planning to add SPI, then it would probably be easier to add the other I/O stuff as SPI rather than parallel. You could also add SD cards for storage instead of Compact flash. Just my $0.02.

_________________
Regards, KM
https://github.com/floobydust

Howdy...

I love the idea of an expansion card.
My personal preference is an SD card rather than Compact Flash, but I guess the Compact Flash cards are pretty cheap as well.
Some kind of sound chip would be nice to get some noise out of the board...
What about I2C, would that be a possibility ?

I'm trying to get a Micro controller mapped to $7F00 (XCS0B) and $7F20 (XCS1B) to get VGA and Sound.
It works most of the time but it's not stable, I'm thinking I need to come up with something else like SPI or Serial.

Keep us updated...

Hi BitWise,

you really put a lot on your expansion, almost more than the SXB board has itself . As for the IDE interface, if you plan to attach only CF cards you should try to get old ones that support the 8-bit Data Bus in IDE-Mode. Actually 8-bit transfers in IDE mode was once a mandatory feature for IDE devices that support the CFA command set (and CF cards are obviously one of these). You can check the appropriate offsets in the result of a IDENTIFY IDE command.

Cheers

Peter