Search found 18 matches

by alastair
27 May 2020, 15:05
Forum: Escape Meta Alt Control Shift
Topic: In memoriam Marcel
Replies: 16
Views: 5105

Re: In memoriam Marcel

Walter, I'm very sorry to hear the news. Even though I've never met Marcel, we had online chats and swapped "war stories" about our early days. I was somewhat aware of his situation, but this still comes as a shock. My deepest condolences to his family and friends. The Gigatron was the inspiration f...
by alastair
04 Apr 2020, 14:58
Forum: Hardware and software hacking
Topic: Using a USB keyboard
Replies: 7
Views: 3512

Re: Using a USB keyboard

One thing that may be a factor here is the contact resistance. I had a lot of issues with my project due to the large current draw and the contact resistance of the barrel connector. The Gigatron has a much lower current consumption, but there are three contact points between the PSU and keyboard (m...
by alastair
24 Jan 2020, 05:07
Forum: Hardware and software hacking
Topic: Gigatron optimisation for a lite version?
Replies: 11
Views: 6135

Re: Gigatron optimisation for a lite version?

I guess it depends what you're to achieve. If the blinkenlights are enough then a simple increment ALU should give you plenty of patterns. Something that simple wouldn't be able to support the video generation though.
by alastair
24 Jan 2020, 01:44
Forum: Hardware and software hacking
Topic: Gigatron optimisation for a lite version?
Replies: 11
Views: 6135

Re: Gigatron optimisation for a lite version?

I always liked the idea of putting the ALU in the ROM and worked on some designs way back in the 80's. I'm bringing one to life after being inspired by the Gigatron. ROMs were pretty small back then, so I had to get creative since a single function to handle two 8-bit values takes up 64k bytes. You ...
by alastair
19 Dec 2019, 18:16
Forum: Hardware and software hacking
Topic: Audio filter values swapped?
Replies: 2
Views: 1709

Re: Audio filter values swapped?

It looks like the frequency response diagram is correct given the Gigatron component values. I think it's just the text that's swapped over. It should probably read "f_H (700Hz) > f_L (160Hz)"
by alastair
19 Dec 2019, 15:36
Forum: Hardware and software hacking
Topic: Audio filter values swapped?
Replies: 2
Views: 1709

Audio filter values swapped?

I've been working on the audio amp/filters on my own project and investigating if the R2R DAC could be rolled in to the low pass filter as the input resistor. It seems to work and this is also the approach taken by the Gigatron. On closer inspection though I'm not sure the filter values look correct...
by alastair
15 Dec 2019, 14:20
Forum: Escape Meta Alt Control Shift
Topic: C74-6502
Replies: 7
Views: 3288

Re: C74-6502

There's quite a few 6502 (and variants) soft cores available for FPGA. The cycle accurate version on Open Cores quotes 10MHz on a Spartan 3E, which is pretty obsolete at this point. You can probably get to 20MHz with the current Spartan 6 or 7.
by alastair
10 Oct 2019, 14:48
Forum: Hardware and software hacking
Topic: High resolution mode?
Replies: 38
Views: 19015

Re: High resolution mode?

The fundamental issue here is the additional state. You only want two states: "Pixel 1" (state A) or "Pixel 2" (state B), but there is also a third state: "Update Pixels" (state C). You can try and adjust the timing and hide state C in the A->B or B->A state transition. This doesn't work though sinc...