Search found 290 matches

by marcelk
Yesterday, 06:47
Forum: Kit assembly
Topic: Gigatron trying to start but doesn't
Replies: 12
Views: 145

Re: Gigatron trying to start but doesn't

The glitchy signal at pins 14 on the right-hand side of the ALU are incoming data bus lines. There's all kinds of different activity on there before they settle, depending on the instruction being executed. Here's one snapshot on one of my boards: DS1Z_QuickPrint19.png DS1Z_QuickPrint22.png On the l...
by marcelk
20 Jul 2019, 19:35
Forum: Escape Meta Alt Control Shift
Topic: Summer + Hebden Bridge, Cambridge and Berlin
Replies: 0
Views: 44

Summer + Hebden Bridge, Cambridge and Berlin

It's time to enjoy summer, so our Gigatron attention will take a step back until September. Some events to watch out for: August 30 to September 8 Wuthering Bytes 2019 festival and OSHCamp Hebden Bridge, UK We won't attend, but Ken Boak plans a presentation featuring the Gigatron! (Saturday, August ...
by marcelk
20 Jul 2019, 18:51
Forum: Hardware and software hacking
Topic: On serialRaw and buttonState
Replies: 0
Views: 77

On serialRaw and buttonState

There are two system variables in page zero that appear to have the same function. At least, you may be fooled into believing that if you simply observe them in a simulator: [$000f] serialRaw and [$0011] buttonState . In reality they have a somewhat different function, and this difference is about t...
by marcelk
20 Jul 2019, 01:36
Forum: Kit assembly
Topic: Gigatron trying to start but doesn't
Replies: 12
Views: 145

Re: Gigatron trying to start but doesn't

I've got a scope and a logic probe, and so far here's what I've determined: Looking at the program counter (U3-U6) I find that PC0-PC7 are counting as expected, PC8 is stuck low, PC9 is stuck high, and PC10-PC15 are stuck low. Where should I start looking next? That's interesting, the system makes ...
by marcelk
20 Jul 2019, 00:43
Forum: Kit assembly
Topic: Gigatron trying to start but doesn't
Replies: 12
Views: 145

Re: Gigatron trying to start but doesn't

What are the chances that there is a defective IC? That would be a first in hundreds of kits, while the symptoms you describe are common. If I don't have a logic analyzer handy, what are my other options for testing? I don't have one either, I just use my scope. But with a bit of care, even a volt ...
by marcelk
19 Jul 2019, 23:31
Forum: Kit assembly
Topic: Gigatron trying to start but doesn't
Replies: 12
Views: 145

Re: Gigatron trying to start but doesn't

That means it's stuck in a software loop that exercises all instructions except subtract. If it has 7 different instruction types in it, that certainly isn't a simple small one! It can't be the memory scan mentioned earlier (ROM address 0020), because that one doesn't have the logical AND and OR ins...
by marcelk
18 Jul 2019, 15:21
Forum: Hardware and software hacking
Topic: Expansion bus
Replies: 51
Views: 3806

Re: Expansion bus

My other interest in this expansion though is actually to see if I could use my Gigatron as an ASCII terminal for my PiDP-11 somehow :-) [I think I want a Gigatron to drive my newly arrived IMSAI 8080 replica kit.] To those of you playing along at home, Jörg's clever signal mapping is implemented i...
by marcelk
14 Jul 2019, 13:37
Forum: Kit assembly
Topic: Gigatron trying to start but doesn't
Replies: 12
Views: 145

Re: Gigatron trying to start but doesn't

4. Your Vcc is beautiful. I don't suspect resetting is an issue. (In that case you'll see the "Power OK" led flicker anyway.)

About the reference sheet: you're right of course: U17-U20 are all the same, and U21-U24 are all the same. Thanks for spotting, I updated the document.
by marcelk
14 Jul 2019, 00:36
Forum: Kit assembly
Topic: Gigatron trying to start but doesn't
Replies: 12
Views: 145

Re: Gigatron trying to start but doesn't

Replying to my own post: I just resoldered every IC pin, diode, and bypass capacitor on the board, and the behavior is unchanged. Of course, I also checked for solder bridges, unsoldered or unseated pins, etc. and found none. I'm running out of ideas... Still this is exactly the right approach to s...
by marcelk
13 Jul 2019, 21:27
Forum: Hardware and software hacking
Topic: New vCPU instructions? (poll)
Replies: 3
Views: 212

Re: New vCPU instructions? (poll)

I would like a bit more guidance to make an informed decision on what (two) items to vote in the poll :) There's no hurry. The poll is open until the end of September :lol: Knowing the expected instruction mix in existing vCPU programs and added value, speedups for example. De concept proposals abo...