Hi,
I'm a beginner ZX81 user (just built a ZX81+38) that started to play around to learn how the hardware is working, and I currently want to understand the details of how the printer works.
I've read that the ZX printer is connected only to very few pins of the expansion port: A2 for addressing, D0/1/2/6/7 for data I/O and RD/WR/IORQ for control signals. I'm a bit surprised that the M1 pin isn't used -- how does that work? I understand that WR probably isn't active at the same time anyway, but wouldn't RD be active during interrupt acknowledge, and then, wouldn't the printer output a signal on the data bus that could interfere with whatever other data is important at the time?
In general: if building some peripheral that connects to the expansion port, is it important to take M1 into account before sending signals to the data bus, or is there a reason that can be ignored?
Thanks,
Staffan
M1 / printer interface
- 1024MAK
- Posts: 5145
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: M1 / printer interface
The ZX81 uses mode 1 (IM 1) so does not care about what is on the data bus. Hence you don’t need to worry about /M1.
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: M1 / printer interface
Thanks!
Makes total sense! I've never actually written any Z80 assembler so I didn't know about the modes, and was also didn't know which one the XZ81 is using. The "CPU Response" chapter of the z80 manual is after the pin descriptions so I never got that far:)
Staffan
Makes total sense! I've never actually written any Z80 assembler so I didn't know about the modes, and was also didn't know which one the XZ81 is using. The "CPU Response" chapter of the z80 manual is after the pin descriptions so I never got that far:)
Staffan