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Sadly, not very good. Glad you could make more!

The new red boards. Same deal as before (see first post in this topic). For now, if you want one, just contact me through the PM system on this site. I will eventually out them up on my web store, but it may take a day or two.

Any chance this RAM board can be modified to work with a C2 or C4?

I'm fairly sure it could, but I don;t have any direct experience with the C2 or C4.

I think MK14HAK (Mike the Kiwi) interfaced the RAM/ROM variant with a C4 :http://www.osiweb.org/osiforum/viewtopi ... t=50#p1800

But I don't know all the particulars.

I'm coming back to this thread because I have a question about the memory expansion in combination with an additional peripheral attached to the expansion port of the C1P, specifically about the DD signal. I have the 32 kB RAM expansion board sucessfully working in a C1P.

Now I came across this floppy controller board: http://bartvoip.co.uk//floppy.htm

I bought a board, assembled it and built a cable to attach it to the expansion port of the C1P on top of the 32 kB memory expansion board, and I couldn't get it to work. After some dicusssions with the producer I realized that the floppy controller board does not implement the DD signal. It is intended to be attached directly to the 6502 bus, without 8T28 buffers in between. So it is clear that the controller board cannot work as-is with the C1P.

I then remembered the article Building a 32K RAM Board on the Glitch Works website. It has a description of a circuit for the Data Direction Generator, consisting of a 74LS00 NAND gate and a 1N4148 diode.

I implemented this circuit as an add-on to the floppy controller board, but it still doesn't work. Of course I can have made a mistake, but before I invest more time and money into troubleshooting this, I wanted to ask whether this is actually the right approach. Should this circuit to generate the DD signal work in combination with the 32 kB RAM board, or would another circuit be necessary?

Thanks
Stephan

You'll need to add a pull-up resistor from DD to Vcc.

Actually no, don't add a resistor, if the memory is working then the DD line is working since it uses the DD line too.

How are you connecting the DD circuit to the floppy board?

This is the sketch for the circuit that I built:
The anode of the diode is supposed to be the DD signal. The IC names and pins refer to the circuit drawing from http://bartvoip.co.uk//floppy.htm linked below.

IC 3 pin 19 is low when the address range of the controller board is addressed.
IC 10 pin 11 is directly the R/W line from the C1P expansion port.

The two NAND gates in my sketch are from a 7400 chip.

That actually looks fine.

You could also try to get Phi2 involved. Bring pin 19 of IC3 to one input of that first NAND gate and bring pin 5 of IC 10 (Phi2) to the other. The rest of the circuit is fine. But it should not really be required in this case.

So you are using the smaller of the two RAM boards, the one without the ROM?

BillO wrote: ↑Mon Oct 10, 2022 1:59 pm That actually looks fine.

You could also try to get Phi2 involved. Bring pin 19 of IC3 to one input of that first NAND gate and bring pin 5 of IC 10 (Phi2) to the other. The rest of the circuit is fine. But it should not really be required in this case.

Thanks, I will try that next, but probably not before next weekend.

BillO wrote: ↑Mon Oct 10, 2022 1:59 pm So you are using the smaller of the two RAM boards, the one without the ROM?

Yes, I'm using the smaller board without ROM.

stm wrote: ↑Mon Oct 10, 2022 5:56 pm Yes, I'm using the smaller board without ROM.

That one actually just passes the DD line straight through.

Do you have a scope?