I've borked it
Re: I've borked it
Hopefully you have plugged in the CPU and ULA the right direction, NOT as shown in the ZX81 manual chapter 25:
https://www.manualslib.com/manual/12017 ... =71#manual
https://www.manualslib.com/manual/12017 ... =71#manual
My ZX81 web-server: online since 2007, running since dec. 2020 using ZeddyNet hardware
http://zx81.ddns.net/ZxTeaM
http://zx81.ddns.net/ZxTeaM
Re: I've borked it
Good grief. Who on earth let that past quality control!siggi wrote: ↑Sat Feb 24, 2024 4:00 pm Hopefully you have plugged in the CPU and ULA the right direction, NOT as shown in the ZX81 manual chapter 25:
https://www.manualslib.com/manual/12017 ... =71#manual
No, I've just got a problem in that I've been pulling chips in and out of sockets for testing combinations that the pins are getting about as weak as my will to continue.
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: I've borked it
I'm trying to figure this out and getting nowhere.
For the HM65256B, looking at the read cycle, both the Chip Enable Access time and the Column Address Hold time, which both run from Chip Enable running low ... are both 150ns. With an "Output hold time from column address of 5ns... it's as if there's no time at all for the processor to actually read any valid data from RAM.
This is making no sense to me.
For the HM65256B, looking at the read cycle, both the Chip Enable Access time and the Column Address Hold time, which both run from Chip Enable running low ... are both 150ns. With an "Output hold time from column address of 5ns... it's as if there's no time at all for the processor to actually read any valid data from RAM.
This is making no sense to me.
All that I've learned - https://msknight.com/bbc/index.html#zx81
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Re: I've borked it
Reading the diagrams on a datasheet is an art
Keep in mind that the diagram itself can be misleading if taken literally. In the real world, the "width" of the various features on the diagram depends on a number of variables, including the clock/bus access speed of the system. Which in the ZX81 are more complex than normal Z80 systems due to the way that the ULA and the Z80 work to generate the data stream for the video.
Okay, the site that I am going to link to is for the 6502, but keep calm, and do have a look, as it does make the timing diagrams make a little more sense. Here's the link.
Back to the Z80 and 32k byte SRAM chips. Most of these all work the same. After all, they were (mostly) all being used for the same function.
Mark
Keep in mind that the diagram itself can be misleading if taken literally. In the real world, the "width" of the various features on the diagram depends on a number of variables, including the clock/bus access speed of the system. Which in the ZX81 are more complex than normal Z80 systems due to the way that the ULA and the Z80 work to generate the data stream for the video.
Okay, the site that I am going to link to is for the 6502, but keep calm, and do have a look, as it does make the timing diagrams make a little more sense. Here's the link.
Back to the Z80 and 32k byte SRAM chips. Most of these all work the same. After all, they were (mostly) all being used for the same function.
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: I've borked it
That's a comprehensive document, but while I can understand what its saying, I'm having trouble identifying the mismatches because some of the chip diagrams are different enough that I can't then make the leap to identify what I need to do, to solve the problem... if that makes sense.
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: I've borked it
Having exhausted all other repair possibilities a more drastic solution is found!
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Re: I've borked it
OK - after much scrumpled pieces of paper, I can't work it out.
Help! Please!
Help! Please!
All that I've learned - https://msknight.com/bbc/index.html#zx81
- 1024MAK
- Posts: 5153
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: I've borked it
"These aren't the droids you're looking for".
If, and it's a big if, I can find a little time at the weekend, I want to try something which may or may not help.
Far too tired now. Dogs woke me at 04:50 just before my alarm was due to go off, as I had to catch an early train to take me to London. Now on the train on the way back.
I'm gonna be going to London next week as well...
Mark
If, and it's a big if, I can find a little time at the weekend, I want to try something which may or may not help.
Far too tired now. Dogs woke me at 04:50 just before my alarm was due to go off, as I had to catch an early train to take me to London. Now on the train on the way back.
I'm gonna be going to London next week as well...
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: I've borked it
It would be wonderful if you could... it's the last piece in the jigsaw for me now.
But I fully understand. Life is difficult enough without commuting to London on top.
But I fully understand. Life is difficult enough without commuting to London on top.
All that I've learned - https://msknight.com/bbc/index.html#zx81