CMS system roms.

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Pernod
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Re: CMS system roms.

Post by Pernod » Wed Jun 13, 2018 3:07 pm

Prime wrote:
Mon May 21, 2018 5:25 am
Pernod wrote:Just whether either of IRQ and NMI lines are connected.
INTRQ -> IC6-LS244 pin 17
DRQ -> IC6-LS244 pin 2

The outputs from those buffers go to Pin 18 to D7, Pin 3 to D6.

This suggests to me that the DRQ and INTRQ are polled by reading an IO register which triggers the gate on the LS244. There is also an LS273 latch on there which I suspect is the drive control latch.
Is anything else contributing to LS244, though I expect not. It looks like it's read at &FC50 with a BIT operation to transfer bits 7 and 6 to the N and V flags. Is any logic connected to either the IRQ or NMI line on the bus connector?

The MTX512 floppy devices do something similar and I never managed to get them working either.
- Nigel

BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, BeebZIF, etc.

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