Zilog Z08470 - Manual (Page 226)

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UM008101-0601 Parallel Input/Output
Set Interrupt Control
If the mask follows bit is high, the next control word written to the port
must be the mask:
In addition, the interrupt enable flip-flop of a port may be set or reset
without modifying the remainder of the interrupt control word. This is
accomplished by issuing the following command:
Used in
Enable
Int.
AND/
OR
High
Low
Masks
Follows
Mode 3 Only
0 1 1 1
MB7 MB6 MB5 MB4 MB3 MB2 MB1 MB0
X X 0 0 1 1 X
Enable
Int.