Search found 319 matches

by at67
15 May 2021, 06:31
Forum: Kit assembly gallery
Topic: I have some problems with my gigatron.
Replies: 9
Views: 89

Re: I have some problems with my gigatron.

The AS6C62256A at 70ns or 55ns should be fine. The HM62256BLP-8 would be borderline at 6.25MHz, it may work, but it would probably be temperamental if it did. The HM628128DLP-5 will work at 6.25Mhz and 8Mhz, but you would need to wire it up according to this thread, (use the 128Kx8 diagram as a refe...
by at67
15 May 2021, 06:22
Forum: Hardware and software hacking
Topic: Expanding ROM space
Replies: 5
Views: 84

Re: Expanding ROM space

Maybe I was not so clear, so I will try to explain a little further. As far as I understand the code of the ROM, SYS_Exec_88 is implemented using LUPs. The following listing of sys_Exec in dev.lst shows this point: Yup, I wasn't clear myself, in ROMvX0, there is going to be much less vCPU code stor...
by at67
15 May 2021, 00:43
Forum: Hardware and software hacking
Topic: Expanding ROM space
Replies: 5
Views: 84

Re: Expanding ROM space

I'm not really completely understanding your train of thought here, so I'll spell out the way I understand Trampolines, LUP, ROM space etc. LUP is a vCPU instruction that is used by vCPU code to access look up tables in ROM, currently the only LUT's in ROM accessed by vCPU code are the Font tables a...
by at67
14 May 2021, 23:05
Forum: Kit assembly gallery
Topic: I have some problems with my gigatron.
Replies: 9
Views: 89

Re: I have some problems with my gigatron.

I would try a crystal smaller than 6.25mhz if available. Your EPROM is a M27C1024-25F1 if I see it right in the picture. That should mean 250ns access time. The Gigatron has a clock of 160ns (at 6.25mhz). So this should not work. Well spotted, also it looks like his SRAM is 120ns, you need 70ns, (o...
by at67
14 May 2021, 20:23
Forum: Kit assembly gallery
Topic: I have some problems with my gigatron.
Replies: 9
Views: 89

Re: I have some problems with my gigatron.

Looking at your photos it looks to me like you have used turned pin headers for the diodes, are you sure that the diodes are making full contact with both sides of the PCB? If even one of the diodes is not making 100% connection to both sides, then the instruction decoding will fail and the boot up ...
by at67
12 May 2021, 20:22
Forum: Hardware and software hacking
Topic: GtForth - Forth on top of the vCPU
Replies: 9
Views: 175

Re: GtForth - Forth on top of vCPU

Thanks for the quick reply! Is there a way to prevent the user from changing modes? Which mode would you recommend in this case? You can keep calling the SYS call SYS_SetMode_v2_80 in your main loop, it will be annoying for the user and frowned upon for most Gigatron applications, but in your use c...
by at67
12 May 2021, 18:50
Forum: Hardware and software hacking
Topic: GtForth - Forth on top of the vCPU
Replies: 9
Views: 175

Re: GtForth - Forth on top of vCPU

I hope GtForth can be useful to you, and any feedback is welcomed! Also, please let me know if you find any bugs or quirks in the program. Works great over here, with a slightly modified print routine you could use the blank scanlines as free RAM as well, (of course if the user manually modified th...
by at67
10 May 2021, 11:24
Forum: Hardware and software hacking
Topic: New vCPU instructions 2.0
Replies: 77
Views: 4481

Re: New vCPU instructions 2.0

Update: I've added the following instructions to the PREFX3 page, the PREFX1 and PREFX2 pages are currently empty. ADDWI <imm>, vAC += 16bit imm, 26+28 cycles. SUBWI <imm>, vAC -= 16bit imm, 26+28 cycles. ANDWI <imm>, vAC &= 16bit imm, 26+22 cycles. XORWI <imm>, vAC ^= 16bit imm, 26+22 cycles. ORWI...
by at67
06 May 2021, 17:29
Forum: Hardware and software hacking
Topic: New vCPU instructions 2.0
Replies: 77
Views: 4481

Re: New vCPU instructions 2.0

Here is what the implementation of PREFX3, it's dispatch page and some corresponding instructions look like now, you'll note the following: Reset to the default vCPU page is now handled in dispatch. vPC fix up is handled in PREFX3. Parsing of the 2nd instruction operand, (PREFX3 instructions always ...
by at67
04 May 2021, 18:34
Forum: Hardware and software hacking
Topic: New vCPU instructions 2.0
Replies: 77
Views: 4481

Re: New vCPU instructions 2.0

I see you've moved code some code to page 0. If I ever complete and merge my Forth, I need a short routine in page 0 (currently 5 instructions). Could you try to leave at least that much space for my purposes? The location isn't important. I used a 3 slot launchpad to move SYS_Reset_88's implementa...