SWTPC GT-6144

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Joined: Nov 24 2013
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I have one of these and was hoping to get it working both for my SWTPC equipment and for my forthcoming Apple 1 replica. I got it wired up and powered it on today, but thus far all I get is:

https://www.youtube.com/watch?v=rCHBsPHH3oM

Wondering if anyone has any pointers on sort of where to go from here -- I see in the forums there are a few people that have had direct experience with these. Many thanks for any advice/etc you can provide!

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Eudimorphodon's picture
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Joined: Dec 21 2003
Posts: 1204
Re: SWTPC GT-6144

According to the assembly manual here:

http://www.swtpc.com/mholley/GT6144/GT6144_Assembly.pdf

The board has a function to blank the screen on power-up, so if that's true a black screen is all you'd expect to see until you run some sort of program to write some data to it. There's a test procedure in the manual that involves setting a jumper to disable the blanking function, so if the board is working properly you'll instead get a random set of pixels. Have you tried that? (and gone through the other verification steps in there?)

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Joined: Nov 24 2013
Posts: 202
Re: SWTPC GT-6144

I ended up finding my error. In my haste, I had assumed the video port at J2 was what I needed to hook up to, just like my CT1024 terminal. But I was wrong -- for some reason video is sent out via Pin 4 of J1, the power supply connector. Strange. And lucky - I had accidentally plugged the power supply with it's -5V pin into that port. Aware of my error now, I've managed to sort it out by creating a new cable that breaks out the video wires. Here's some pics:

https://drive.google.com/file/d/0B4pq0-BHd2x6ZTN0b0NJZ3Mwa0k/view?usp=sharing
https://drive.google.com/file/d/0B4pq0-BHd2x6NnZWQXFpM3JYeUk/view?usp=sharing

And with reverse video jumper toggled just to see if it works:

https://drive.google.com/file/d/0B4pq0-BHd2x6ckk5MHlQaWhYVUE/view?usp=sharing

Very cool to see this thing operating, sort of. The manual says I'm supposed to get a random series of blocks every time I power up, however it's the same screen.. so I'm not sure if the RAM is working right or if that's just how it is in the absence of the screen blanking circuit (which I've disabled for now) being enabled.

I've not been able to find another person online with one of these to compare and see in action. I'm hoping to be able to use this board with both my Apple I replica (in progress) and my SWTPC gear. If anyone out there has actual info on how to interface it with an Apple 1, I'd be very appreciative. So far I've only found some general references to it in magazines, just mentioning the ability but not the how.

OrionSoft's picture
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Joined: Jan 24 2017
Posts: 8
Re: SWTPC GT-6144

Nice photos !
Here is the instruction on how to interface it with Apple 1
http://www.applefritter.com/?q=node/2818

I don't have this graphic card, but I tried to convert the original SWTPC test program for this graphic board, into 6502 code for the Apple 1
Here is the code, I can't warranty this will works, but hopefully ...
0300: A9 00 8D 0B D0 A9 FF 8D 0A D0 A9 2C 8D 0B D0 A2
: 00 A0 00 8A 8D 0A D0 98 09 80 8D 0A D0 C9 DF F0
: 04 C8 4C 17 03 8A C9 3F 10 04 E8 4C 11 03 A2 05
: A0 0D A9 8E 85 00 A9 03 85 01 20 5E 03 A2 1B A0
: 40 A9 F3 85 00 A9 04 85 01 20 5E 03 A2 00 A0 00
: A9 E3 85 00 A9 05 85 01 20 5E 03 4C 5B 03 86 02
: 84 03 A0 00 20 86 03 C9 FF F0 1A 18 65 02 09 40
: 8D 0A D0 20 86 03 C9 FE F0 EA 18 65 03 09 80 8D
: 0A D0 4C 73 03 60 B1 00 C8 D0 02 E6 01 60 00 0A
: 0B 0C FE 01 0A 0C FE 02 0A 0C FE 03 09 0C FE 04
: 09 0C FE 05 09 0C FE 06 08 0C FE 07 08 0C FE 08
: 08 0D FE 09 07 0E FE 0A 05 0F FE 0B 04 05 0F 10
: FE 0C 04 05 0F 10 FE 0D 05 0F FE 0E 05 0E FE 0F
: 06 0D FE 10 07 0C FE 11 07 0C 19 FE 12 08 0C 0D
: 16 17 18 19 1A 1B 1C FE 13 08 0C 0F 17 18 19 1A
: 1B FE 14 08 0C 10 16 17 18 19 1A 1B 1C FE 15 08
: 0C 11 15 1D FE 16 08 0C 12 14 19 1E FE 17 08 0C
: 13 19 1E FE 18 08 0C 13 19 1F FE 19 09 0A 0B 0D
: 13 19 1F FE 1A 05 0F 13 1F FE 1B 03 04 06 07 11
: 14 19 1F FE 1C 02 08 13 14 19 1F FE 1D 02 08 14
: 19 1E FE 1E 02 08 14 1E FE 1F 02 08 14 1E FE 20
: 02 08 14 1E FE 21 02 08 09 0A 0B 0C 0D 0E 0F 10
: 11 12 13 14 15 1E FE 22 02 1D FE 23 02 1D FE 24
: 02 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 1D
: FE 25 02 08 15 1D FE 26 02 08 15 1B FE 27 02 08
: 15 1A FE 28 02 08 15 1A FE 29 02 08 15 1A FE 2A
: 02 08 16 17 18 19 1A FE 2B 02 08 FE 2C 02 08 FE
: 2D 02 08 FE 2E 02 08 FE 2F 02 08 FE 30 01 02 08
: FE 31 01 02 08 FE 32 01 02 08 FE 33 01 02 08 FE
: 34 01 02 08 FE 35 01 02 08 08 FE 36 01 02 08 FE
: 37 02 08 FE 38 02 04 05 06 07 FE 39 02 03 FE 2A
: 15 FE FF 00 1A 1D 1F FE 01 17 FE 02 13 FE 03 10
: FE 04 0D FE 05 0B FE 06 0A FE 07 08 FE 08 07 FE
: 09 06 FE 0A 05 06 07 FE 0B 04 05 06 07 0B FE 0C
: 04 05 06 07 0A FE 0D 03 06 09 0A FE 0E 07 08 09
: FE 0F 02 08 09 0A 0B 0C 0D 0F 10 FE 10 09 0A 0B
: 0C 0D 0E 0F 10 11 12 13 FE 11 02 09 0A 0B 0C 0D
: 0E 0F 10 11 12 13 14 15 FE 12 02 05 07 0B 0C 0D
: 0E 0F 10 11 12 13 14 15 16 17 FE 13 04 05 06 08
: 0C 0D 0E 0F 10 11 12 13 17 FE 14 02 06 07 0A 0B
: 0C 0D 0E 0F 10 11 12 13 14 17 FE 15 07 0B 0C 0D
: 0E 16 18 1C FE 16 03 18 19 1A 1B 1C 1D 1E 1F 1F
: FE 17 04 16 19 1A 1B 1C 1D 1E 1F 1F FE 18 05 19
: 1A 1B 1C 1D 1E 1F 1F FE 19 06 1C 1D 1E 1F 1F FE
: 1A 07 1D 1E 1F 1F FE 1B 08 1E FE 1C 0A FE 1D 0B
: FE 1E 0D FE 1F 10 FE 20 13 FE 21 17 FE 22 1A 1D
: 1F FE FF 01 2C FE 02 58 FE 05 04 FE 0A 1E FE 0C
: 40 FE 0D 30 FE 0F 44 FE 14 58 FE 19 4C FE 1E 3A
: FE 20 06 FE 26 30 FE 31 0A FE 34 34 FE 35 1C FE
: 3B 02 2A FE 3E 42 FE FF

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I'm young retro computing geek, and indie game developer on retro consoles.
http://orionsoft.free.fr/

OrionSoft's picture
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Posts: 8
Re: SWTPC GT-6144

I just made a quick hack to Pom1 (Apple 1 emulator) to emulate the GT-6144 board, and my test program seems to work Smile

(match this http://www.swtpc.com/mholley/GT6144/GT6144_TV.jpg )

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I'm young retro computing geek, and indie game developer on retro consoles.
http://orionsoft.free.fr/

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Joined: Nov 24 2013
Posts: 202
Re: SWTPC GT-6144

Thank you very much for the info!!

That screen you got certainly looks correct!

I'm wondering -- are there any records of people creating actual games/software using the GT-61? I'm surprised I've not been able to google one other owner or example of actually using the thing beyond the Star Trek screen for SWTPC. Hoping maybe Apple 1 users were a bit more motivated. Smile

Eudimorphodon's picture
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Joined: Dec 21 2003
Posts: 1204
Re: SWTPC GT-6144

Man,SWTPC's 1976 catalog actually seems to have the best description of how to program the crazy thing. (While their 1978 catalog lists a couple trivial games that support the board.)

I'm guessing the best source of any other software that might be out there for it would be the FLEX users group; their website has the two games listed in the SWTPC catalog directly downloadable, and there might be more in their .dsk collection somewhere. Obviously this would be 6800 software. I strongly suspect the number of these things that were ever connected to an Apple I could easily be enumerated using the toes on one person's foot, but I guess you never know.