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PC-Sprint on the Tandy 1000A?

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theturtle32

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I have a Tandy 1000A, put a 16MHz-rated NEC V20 into it, and bought all the parts to build a PC-Sprint board to run that V20 a bit faster than 4.77MHz. And then I went looking on the motherboard for the Intel 8284A chip and can't find it... does anyone know what is going on here? Did Tandy integrate that functionality into a custom IC? Is there any hope for PC-Sprint on a 1000A?

This note I found hints that it may be possible, but perhaps a different implementation of the mod is required?
https://github.com/reesclissold/pc-sprint/blob/master/Everything Else/Documents/pcspnt.txt#L7
 
Long story short, no, the PC-Sprint isn’t applicable to the 1000A. It uses a proprietary ASIC that has the guts of a 8284a and several other components integrated into it; it’s very similar to the ASIC that performs a similar task in the 1000SX, EX, and HX but lacks the 7.16mhz turbo speed.

I’ve pondered the question of how to accelerate one of those later models myself, and I’m not sure it’s really doable in a “PC-Sprint”-ish way unless you replaced that whole ASIC with a daughter board because I’m pretty sure some of the connections you’d want to hijack are internal to it, but I very well could be wrong,
 
I did a bit of Googling and that note on the GitHub about them selling a “PC-Sprint” for the 1000A does appear to be true, but it’s always just a one sentence blurb in an ad, I wasn’t even able to find a review, let alone a picture. If anyone ever finds one of these white whales please photograph it extensively for possible cloning!

(My guess is it’s a daughterboard that essentially contains a discrete component clone of the timer chip’s internal circuitry with the speed switch incorporated and you remove the original ASIC?)
 
Do you really need to replace the ASIC? I thought you might get by with a modified version of PC-Sprint which has a discrete 8284 which is used for the CPU acceleration and otherwise passes through the timing from the ASIC for unaccelerated operation.
 
Great Hierophant said:
Do you really need to replace the ASIC? I thought you might get by with a modified version of PC-Sprint which has a discrete 8284 which is used for the CPU acceleration and otherwise passes through the timing from the ASIC for unaccelerated operation.
Click to expand...

I would need to dig into exactly where the PC-Sprint fits into the schematic again but my impression was essentially that some of the necessary inputs/and/or/outputs to it are buried inside the ASIC and therefore you can’t just put another 8284 in “in parallel” the same way. I don’t have the datasheet for the 1000A’s version of the chip handy but the SX/EX/HX version has a pretty big chunk of the bus arbitration circuitry mixed up with the clock generation functions.
 
Eudimorphodon said:
I did a bit of Googling and that note on the GitHub about them selling a “PC-Sprint” for the 1000A does appear to be true, but it’s always just a one sentence blurb in an ad, I wasn’t even able to find a review, let alone a picture. If anyone ever finds one of these white whales please photograph it extensively for possible cloning!

(My guess is it’s a daughterboard that essentially contains a discrete component clone of the timer chip’s internal circuitry with the speed switch incorporated and you remove the original ASIC?)
Click to expand...
When I was in high school I modified our Tandy 1000 Original with a turbo button I ordered mail order from the back of Computer Shopper I think. As I recall it had a tiny daughterboard, the toggle switch and a new clock crystal. After reading the linked document, I'm sure it was the PC-SPRINT but you have to have the original 1000 prior to the model A, otherwise it's not compatible. This is exactly what I did on my 1000 back in the 80s.
github.com

pc-sprint/Everything Else/Documents/pcspnt.txt at master · reeshub/pc-sprint

The PC-SPRINT 8088 PC Accelerator Board by Doug Severson - reeshub/pc-sprint
github.com github.com
 
Last edited:
theturtle32 said:
I have a Tandy 1000A, put a 16MHz-rated NEC V20 into it, and bought all the parts to build a PC-Sprint board to run that V20 a bit faster than 4.77MHz. And then I went looking on the motherboard for the Intel 8284A chip and can't find it... does anyone know what is going on here? Did Tandy integrate that functionality into a custom IC? Is there any hope for PC-Sprint on a 1000A?

This note I found hints that it may be possible, but perhaps a different implementation of the mod is required?
https://github.com/reesclissold/pc-sprint/blob/master/Everything Else/Documents/pcspnt.txt#L7
Click to expand...
I found a picture of the 1000A version, page 26 of the PDF, 24 of the magazine. It's significantly different from the regular PC-SPRINT.
I don't think it's high res enough to reverse engineer. :/
 
ericmnv said:
I found a picture of the 1000A version, page 26 of the PDF, 24 of the magazine. It's significantly different from the regular PC-SPRINT.
I don't think it's high res enough to reverse engineer. :/
Click to expand...
I have a 1000SX with a 8 MHz V20. You may get your chip to turn out 20 MHz but your board's system xtal is still 4.7 MHz. Also, you need to consider wait states. Personally, I wouldn't waist my time as the performance gain on that 8-bit system will be negligible,
 
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