CPU I/O Registers - Plus/4 Encyclopedia



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CPU I/O Registers

Category
Programming/Assembly

Topic

Address	B7	B6	B5	B4	B3	B2	B1	B0	Description
$0000	...	...	...	...	...	...	...	...	Data direction register (PDIR)
$0001	...	...	...	...	...	...	...	...	8 bit I/O port (PORT)

8 bit I/O port:
B7 $80 : serial DATA in
B6 $40 : serial CLK in
B5 $20 : unused (always 0)
B4 $10 : cassette read
B3 $08 : cassette motor (0 = on, 1 = off)
B2 $04 : serial ATN out
B1 $02 : serial CLK out / cassette write
B0 $01 : serial DATA out