Posted By
MikeZ
on 2016-03-08
13:13:53
 |  Re: Ultimate Map V1.8
The plus/4 schematic clearly shows that 6551 pin 9 (CTS) is permanently grounded. So CTS is always true at the 6551.
Any manipulation of CTS is done when FD01 is copied to RAM at 07D4. Where it retains its bit #4 location.
During the IRQ cycle FD01 is copied to working RAM at 07D4. Code at EA89 shows toggling of Bit 4 as CTS.
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