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5-11
H Message Timing
The Message Communications Enabled Flag must be used as an execution condition for the Master
when IOWR is used. Be sure this flag is ON before executing IOWR. If IOWR is executed when this flag
is OFF, a Special I/O Unit error may be generated for the Master.
Execution
condition
Message
Communications
Enabled Flag
(@) IOWR
C
S
D
B
A
25506
Equals Flag
B
A
1. IOWR is executed when the execution condition is met and the Message Communications Enabled
Flag is ON.
2. When IOWR is executed, it is self-held by bit B.
3. When IOWR is completed, the Equals Flag turns ON and the self-holding bit is cleared.
Note 1. If IOWR ends in an error, the Equals Flag will not turn ON, so the self-holding bit will remain
ON.
Note 2. The Equals Flag is also affected by the execution of other instructions, so be careful not to use
any other such instructions between IOWR and the Equals Flag.
CompoBus/D Communications Card Operations Chapter 5