System 6 Driver 6821 PIA Issues

[Rav]

Hey Guys, after days of trying to work this out, I gotta see if anyone has fresh ideas...



I have PCB Set 1 and PCB Set 2, both System 6 right? Im using Leons test Rom so we're pulsing high low every second...



I know Set 1 is OK, and know that the driver pcb from set 2 will happily high/low pulse on the 6821s so everything slooking good...



Now plug either driver board into set 2's MPU pins 2-17 of both IC5 and IC10 6821 PIAs show either high or low but not pulse or activity - the data lines are happily H/L Pulsing!



Its not the 6821s or indeed therefore a driver pcb issue...



testing the pins on the connector of the MPUs from 1-40 Im getting the same activity on the probe so it LOOKs like both pcbs are outputting the correct signals on the connectors (all replaced btw!)



So, I cant see what the issue is - maybe a timing on these pins? Its doing my nut in and every day the Slam looms closer!



I guess i need to repat the excercise of reading the pins 1-40 when the drivers are connected on both pcbs next? Or does someone know what makes the 6821 pins 2-17 toggle and pulse?

Thanks in advance I'm completely lost!

R!

 

[Moonraker]

Pins 2-17 are two 8 bit bi-directional data bus/buffer for communications. Pins 2 to 9 are peripheral interface A and pins 10 to 17 are for peripheral interface B. More information at http://www.datasheetcatalog.org/datasheet/motorola/6821.pdf



I still recon your problem may be a ROM problem or ROM addressing issue... Are you able to try the boards in another system 6 game?

 

[Rav]

Thanks for the tip - not half an hour ago I manged to solve it. Turned out that the 02 signal on pin 9 was also touching pint 10 on the 40 way connector which was corrupting D0 data line - took AGES to find but ended up checking pretty much every address bus trace and data line but got there in the end! PHEW!

 

[Sgt GrizZ]

Good work soldier