Sinclair ZX80 / ZX81 / Z88 Forums

A Spec-chum of mine here in Germany wants to drive some relays from his Spectrum (some kind of programmable robotic arm is his aim I believe). I said I'd ask some questions for him as I don't think he can speak English that well. He seems fairly competent with electronics, at least competent enough to make this I/O device, which was detailed in a 1984 German mag: He has asked me how does he make the relays work from a BASIC program. I have no idea, perhaps someone else has an insight.

As you are asking the question in relation to a ZX Spectrum, I have moved this to the ZX Spectrum hardware area.

On a ZX Spectrum, use:
OUT a,d

Where a is the address the interface is mapped to, and d is the data byte you want sent to it. Both are in decimal. See the manual for more information.

To read data from the inputs, use:
LET d=IN a

Where a is the address, and d will be given the data byte read by the Z80 from the interface inputs.

The above assumes that the selection jumper to IC N11 is wired to /IOREQ.

If the interface was to be used on a ZX81, then the selection jumper can be wired to /MREQ. As ZX81 BASIC does not have an OUT command, POKE is used instead.

We don’t use /MREQ for the ZX Spectrum, because the memory map on the ZX Spectrum is full, and it would conflict with accessing memory.

Mark

I work the address out to be 0x3FE1 or 16353 decimal.

On a ZX Spectrum address line A0 has to be high (1) otherwise the ULA will respond. Hence 0x3FE1 or 16353 decimal.

Mark

Ah yes, it's ZX Spectrum related, sorry.

Excellent, I'll see if he has the German version of the manual and point him at the IN/OUT section and forward your info.