Search found 37 matches

by PurpleGirl
Yesterday, 18:24
Forum: Hardware and software hacking
Topic: Modified Gigatron Design Ideas
Replies: 32
Views: 1793

Re: Modified Gigatron Design Ideas

I've been thinking about Ben Eater's "video card" design. I was pondering how to modify it to where the syncs could be modified by software. I think I've discovered a way to do that. Instead of using hardwired logic gates, a register and a digital comparator would be better. So the pixel counter set...
by PurpleGirl
Yesterday, 18:22
Forum: Hardware and software hacking
Topic: Opcode mods
Replies: 6
Views: 301

Re: Opcode mods

A clarification. I've never said that the CPU has any hidden states. My idea to piggyback onto a NOP instruction is only for external devices. For instance, if an external video controller is used and there is the chance of losing the syncs or not knowing where the raster is, one of the spare NOPs c...
by PurpleGirl
20 Dec 2019, 07:22
Forum: Escape Meta Alt Control Shift
Topic: C74-6502
Replies: 6
Views: 259

Re: C74-6502

marcelk wrote:
14 Dec 2019, 16:31
I doubt Drass is reading this forum. But you can propose your enhancement in the design thread on the 6502 forum: http://forum.6502.org/viewtopic.php?f=4&t=3493
No, but I think Dieter does. He has read some of my posts.
by PurpleGirl
19 Dec 2019, 08:41
Forum: Hardware and software hacking
Topic: Opcode mods
Replies: 6
Views: 301

Re: Opcode mods

Another mod that came to mind, though likely not attractive to use, would be replacing most of the instruction decoder with a ROM. The instruction register can drive the address lines and the data lines drive the control lines. So this replaces the logic with an instruction map. There would be no sp...
by PurpleGirl
15 Dec 2019, 17:48
Forum: Escape Meta Alt Control Shift
Topic: C74-6502
Replies: 6
Views: 259

Re: C74-6502

Yeah, but the FPGA in the Eclaire goes about 50 Mhz. The Eclaire implements the majority of the Atari 800, etc., in FPGA. So the "Sally" 6502, Antic, GTIA, PIA, and 2 Pokeys are all on a single chip. The original Ataris only use 1 Pokey for ports, keyboard, and sound. However, arcade games and homeb...
by PurpleGirl
14 Dec 2019, 21:04
Forum: Escape Meta Alt Control Shift
Topic: C74-6502
Replies: 6
Views: 259

Re: C74-6502

Yeah, thanks, that would be a good idea. Adding the /halt line to the design would increase compatibility with vintage systems. The Ataris that used the 6502 mostly used the "Sally" variant with the halt pin, though some of the older Ataris didn't use it. So they got MOS to add the halt line to simp...
by PurpleGirl
13 Dec 2019, 21:30
Forum: Escape Meta Alt Control Shift
Topic: C74-6502
Replies: 6
Views: 259

Re: C74-6502

Yes, that is neat, and I bet it could go even faster when implemented in FPGA (and one implemented that way will do about 50 Mhz). But I see one shortcoming that should be easy to address. It seems to lack the "Sally" compatibility, so it won't work with an Atari computer without adding 4 additional...
by PurpleGirl
05 Dec 2019, 15:50
Forum: Escape Meta Alt Control Shift
Topic: Thinking of creating a custom CPU
Replies: 0
Views: 119

Thinking of creating a custom CPU

I am not committed yet, but I've been considering a custom CPU. I am only in the crude planning stages about the architecture I'd want. I'd likely need to learn how to do FPGA, especially if I were to do 32 or more bits. So I'd need to get accustomed to using FPGA design software and Verilog/HDL. No...
by PurpleGirl
25 Nov 2019, 06:04
Forum: Hardware and software hacking
Topic: Modified Gigatron Design Ideas
Replies: 32
Views: 1793

Re: Modified Gigatron Design Ideas

So a 377 or 2 161's might be better for what I have in mind, though a tristate buffer might work if the data is streamed. So it depends on the application. But adding opcodes, I think I'd want an X-Out rather than a load.
by PurpleGirl
24 Nov 2019, 01:39
Forum: Hardware and software hacking
Topic: Modified Gigatron Design Ideas
Replies: 32
Views: 1793

Re: Modified Gigatron Design Ideas

Thanks. I'll read that. But I see the opcode thing as not too hard. Make X-out closer to another register. I see, so Mr is the reset, and holding the clock low causes it to act more like a register. If I were going to mod it and make it more like a register, I'd probably be more interested in a 244 ...