Bus resistors in STM

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PeckPeekPoke
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Re: Bus resistors in STM

Post by PeckPeekPoke »

DoG wrote: Sun Jul 11, 2021 9:50 pm C070522.png

I found some schematics on the C070522. It "should" be the same for C070523 I guess. Anyhow, it seems that RP2, RP3 and RP8 are the address bus and RP7 and RP9 are the data bus since they are pulled high to 5V. All of these are 10K.

RP2 is only 8 pin? (7 resistors and the common). All the others are 8pin resistor arrays. You have to check if that is the case on your board.

I really don't know why they have added some pull down resistor as well on RP1 and RP4 (4.7K). RP1 is 8pin on schematics and an additional lonely resistor (maybe R81?).

RP2, RP3, RP8, RP7 and RP9 is what we usually change on these these Ataris.
Thanks for checking the CO70522 schematics! I think there are some differences.

The C070523 I've got has only 9-pin resistor arrays in the places we've discussed, thus RP1 on my board is a 9-pin.
On my board, RP8 is next to the CPU, with R81 to its left, and it is also a 9-pin array. Perhaps it was more efficient for Atari to use 9-pin parts everywhere in the build, but leave a pin unused rather than stock two different parts? :?

Many thanks... :geek:
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