470B usage on 600RevD / 502

Post Reply
MK14HAK
Posts: 356
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

470B usage on 600RevD / 502

Post by MK14HAK »

I have a 470B that started life as a printer port card but I have populated it to use as a FDC. Its a real birds nest with motor control,dual sided ,data sep mods etc - but reliable. I even recently dropped a pile of books on it but it keeps going and has been in use on and off with 8" and 5" and 3.5" drives for a few years on my 600RevD.
This week I connected it up to my SKIT502 now with 32K ram. Not booting.
Then 8T28 changed to 8T26 for data inversion compatibility with 502 ! - tk0 header data still reading wrong. It seeks TK0 and loads head OK with $F706G. (Cegmon) Unloads head with resultant incorrect data read.

600RevD has OSI bus signals B1-B3 ;B13-B24; B29,B30 ;B35,B36 ;B39,B41 all not connected. I dont see any problems with having these connected on the 502. (Note sure where WAIT goes yet on 502 ?) Address lines A2,3,6,7 are unused on 470 as with IRQ and NMI

Im going to re check connectors ,VMA, 02-VMA, 8T26s and timing. (swapped back to 600RevD with buffers changed and still boots the same drive and disk fine)
It must be reading PIA correctly as it senses tk0 and index. It also gets buffer read ready from ACIA. Maybe its timing? or something with the OSI 48P bus signals, thats still new to me, Ive missed.

Ideas?

Update:
Thanks Phil, -scrape the oxide from bus pins then de-oxit .Now working. D&N next.

All that's required to swap 470 between C1 and C4 is the 8T28/26 buffer change.
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator
Post Reply