Search found 20 matches

by HGMuller
22 May 2018, 05:02
Forum: Hardware and software hacking
Topic: Programming in native assembler
Replies: 0
Views: 5373

Programming in native assembler

As I plan to write a chess program for the Gigatron, speed is very important to me. I don't want to lose a factor on the interpretation of an intermediate language like GCL, so I directly want to write native code, to put it in the EPROM. This of course burdens me with the task of video generation i...
by HGMuller
21 May 2018, 18:06
Forum: Hardware and software hacking
Topic: Blue LEDs for Power and Blinkenlights
Replies: 5
Views: 5403

Re: Blue LEDs for Power and Blinkenlights

Well, it seems that blue LEDs run at ~3.3V, so only ~1.5V left over the resistor, instead of ~3.0V. So if you don't change the resistors, they would get half the current of the red LEDs. But that just means they burn a little less bright than they could. To the eye a factor 2 in light yield is barel...
by HGMuller
21 May 2018, 17:43
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 16792

Re: Extending the Gigatron instruction set

Schematic of the modified bus-access decoder:
giga7.png
giga7.png (28.38 KiB) Viewed 7252 times
by HGMuller
21 May 2018, 09:09
Forum: Hardware and software hacking
Topic: Blue LEDs for Power and Blinkenlights
Replies: 5
Views: 5403

Re: Blue LEDs for Power and Blinkenlights

I would not expect the resistor value to be very critical: it controls the current through the LED, and thus how brightly it emits. As long as you don't exceed some maximum current, having a 'wrong' value would just result in a different brightess. 2mA doesn't sound like a lot to start with (power d...
by HGMuller
20 May 2018, 21:05
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 16792

Re: Extending the Gigatron instruction set

Iteration 2 For simplifying decoder logic, it turned out to be better to invert the meaning of IR2. In addition, rather than selecting X as high address on ALU instructions whenever IR1 was high, it turns out to be more convenient to do this only when IR1 and IR0 are both high. This takes only one ...
by HGMuller
17 May 2018, 18:55
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 16792

Re: Extending the Gigatron instruction set

A tentative redesign: IR5-7 keep the meaning they have now: primarily selecting ALU function, or generating the jump (!J) and store (!W) signals. IR3-4 select the destination register, i.e. IR2 will be decoupled from the 3->8 decoder, so that this effectively becomes a 2->4 decoder. The outputs will...
by HGMuller
16 May 2018, 20:03
Forum: Hardware and software hacking
Topic: Second scanline disable for double the performance:
Replies: 4
Views: 4227

Re: Second scanline disable for double the performance:

Indeed, this is a useful trick. I am working on a Chess program, and my plan was to skip 3 out of 4 lines while the program is thinking. That would still leave a recognizable chess board, and have the advantage that it would become immediately obvious when the program is done thinking, and it is you...
by HGMuller
16 May 2018, 19:46
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 16792

Re: Extending the Gigatron instruction set

Well, since X is a counter [X++,D] should also be easy to realize. The main question is which opcodes to repurpose. Currently multiple addressing modes are only found on instructions with ACCU as destination, and to a lesser extent with OUT. In that design it would make sense to only add new modes t...
by HGMuller
14 May 2018, 07:26
Forum: Hardware and software hacking
Topic: Extending the Gigatron instruction set
Replies: 22
Views: 16792

Extending the Gigatron instruction set

One of the nice things about having a CPU built from TTL components is that you don't need to consider it a 'given', but can change the architecture to meet your needs. Want another index register, or a second accumulator? Just grab your soldering iron! Of course adding new features to the architect...
by HGMuller
14 May 2018, 05:57
Forum: Escape Meta Alt Control Shift
Topic: Lets see if this pbpBB system works for us
Replies: 4
Views: 4739

Re: Lets see if this pbpBB system works for us

Great! I was really missinge a place like this, where we could share ideas about the Gigatron. 8-)