Hi
Despite the low activity on discussion of the I/O extension board I have a question that someone might have the answer to. I've read the manual but I'm not 100% sure that I got things right. My question is : Is it possible to use 64k ram (upper or lower)and still have some extra io-pins or is it as I suspect either ram or io? Could memory board that ships with zx1281 be connected to the ext io-board and if so can someone give a hint of how to adress it (hint for hardware schematic and code snippet to get the idea). Might sound that I want others to do my job but I'm an hobbyist so I still need to pointed in right direction.
Any help would be appreciated
Regards Hucke

As you suspect the I/O Extension board can either be used for I/O or for RAM. The active low RAM_EN pin (#20) decides which one.

I'm not sure what memory board you are talking about that ships with the ZX-1281. Do you mean the Oak MicrosZX-1281e/ZX-1281ne? The schematic for this RAM duagherboard is on page 23 of the ZX-1281e/ne documentation.

Regards,
Mike

Thanks for such rapid response. I have OakMicros 64k Ram-card shipped with zx1281e from you. My problem is that I need extra pins but also more ram. If I can find out how to piggyback this card on the 128 ext card how do I get the zx to be aware of the extra ram? Will Option ExtRamConfig On be enough ?
Regards Hucke

The ZX-1281e has 32 I/O lines. If you need more, you may want to read AN-203 I/O Expansion Techniques.

The mega1281 on the ZX-1281e can access up to 64K of RAM (16-bit address) using "Option ExtRamConfig On". If the option id off then only the internal 4K RAM is available. External ram is accessed using 19 I/O lines from ports A, C, and G. If you want more than 64K, you will need to employ "bank switching" and additional I/O lines to switch the bank.

The RAM daughterboard is hard-wired for 64K. The extension I/O card has up to 128K that is bank-switched via the A16 pin. It may be possible to combine two extension I/O cards to provide a total of 256K which would require 2 or 3 external lines for bank switching.

Hi
Thanks for reply. I think I got the picture now. The PCF8574A I/O Expander seems to be the easiest way to get more pins.
Regards Hucke

Hi again!
I've decided to use io-extender to get more pin's and use the om128-ext for memory. I've wired up with a ds1307 card from Futurlec and it works ok UNTIL I ground pin 20 on om128-ext to enable extra memory. The clock stop's and the processor seems to hang. I've checked and rechecked electric wiring and tried with/without enabled memory with same result so I don't think thats a problem. Any idea what could be wrong? Is I2c in anyway affected of the ext board??
Any help will be appreciated
Regards Hucke