| Attachment | Size |
|---|---|
 The mystery cable | 2.69 MB |
Someone once installed a mysterious wire with a plug on the end of it in my Apple II. It's connected to pin 13 of the 74LS04 chip in the C-11 and appears to control DMA. Does anyone recognize this extension and could tell me what it was used for?
It looks indeed like an extension to the /DMA signal into pin C11-13. Is the pin on the chip pulled up to isolate it from the circuit board?
Normally, any peripheral (like a SCSI card) that needs to use DMA already has access to the /DMA signal on pin 22 of the I/O slot, so running a flying lead for that signal is unnecessary. The only thing I can think of is a CPU accelerator with no slot card, like a Zip Chip, that needs the /DMA signal for cache invalidation.
The pin is not isolated. The connections on the PCB appear to have not been modified. The /DMA signal available in the sockets is working properly.
The computer arrived in this condition, and the included cards likely didn't use this cable either.
CPU is 6502 from Synertek