Search found 32 matches

by alastair
17 May 2022, 17:12
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

I've only used GALs (which are reprogrammable) before, but I thought that PALs were OTP? I usually use GALs, specifically the ATF16V8B for development. I try and stick within the original PAL specs so you could build it with the vintage parts. I do have some NOS PALs for another project, but I stil...
by alastair
14 May 2022, 03:45
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

Mostly routed. I was going to test the new design on a breadboard, but the only real change are the PALs. These can be reprogrammed so most of the debugging will be in firmware... assuming I didn't screw up the schematic. The ATtiny85 is on the board for the basic Pluggy, so it can be built to match...
by alastair
10 May 2022, 17:36
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

Initial chip placement. The connectors and associated components haven't been added yet; they would go along the bottom edge. The gap is for the Pluggy Reloaded components. I left the option to use the existing Pierce Oscillator/6.25MHz crystal or you can use the can oscillator and divider (bottom l...
by alastair
05 May 2022, 17:47
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

Video Repeater : https://forum.gigatron.io/viewtopic.php?t=303 I think I'm going to go with the video repeater, at least layout the components on the board as an option. The FIFOs are kind of pricey but not crazy and they are still in production. The ALU won't fit in a pair of 16L8 PALs. It probabl...
by alastair
04 May 2022, 15:13
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

I was leaning towards ... this Scratch that. There's only 6 bits available because I still need the H & V sync bits. That would be 3 bits each per pixel and the basic 1 bit RGB colors. These can be maxed out (>1V) to fully saturate the colors and get the "classic" 8 color palette.
by alastair
04 May 2022, 13:12
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

I was leaning towards a 74HC244 ganged to this with a 3PDT switch to select between the two resistor DACs. I could also look at using some 74HC670 register files as a RAMDAC and have a way to load the palette colors during blanking. Anther option with a RAMDAC is doubling up again, so 4 pixels per c...
by alastair
04 May 2022, 00:12
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Re: Gigatron Clone Ideas

Video Repeater : https://forum.gigatron.io/viewtopic.php?t=303 I was debating the video repeater but might not go that far. 25MHz oscillator with jumper selectable /1,/2 and /4 clock options using 74LS74. This is probably how I will go. I need a symmetrical clock from a flip-flop with a Q and ~Q ou...
by alastair
03 May 2022, 21:08
Forum: Hardware and software hacking
Topic: Gigatron Clone Ideas
Replies: 15
Views: 490

Gigatron Clone Ideas

I've been thinking about doing a Gigatron clone for some time and finally sketched out an initial plan. This would be binary compatible with the existing code base, but with some of the newer ideas integrated on a new PCB. These include: * Pluggy Reloaded * 6-bit Audio * High Resolution as an option...
by alastair
15 Aug 2021, 14:54
Forum: Hardware and software hacking
Topic: Character Sets
Replies: 7
Views: 2715

Re: Character Sets

I assume this would be the latest font - https://github.com/kervinck/gigatron-rom/blob/master/Core/font_v4.py I'm not too familiar with the build process, but you can checkout the repo and either modify this file or create a new version and pull that in to the build. There should be info in this for...
by alastair
12 Jul 2021, 13:46
Forum: Hardware and software hacking
Topic: whole board with 74LS
Replies: 7
Views: 3610

Re: whole board with 74LS

The passive components of the Pierce oscillator circuit are designed for CMOS. E.g. the feedback resistor is 1M ohm. For a 74LS04 you will need to drop this significantly to around 1k ohm. This is an example I built using F-series TTL chips. You may need to play with the values of the resistors and ...