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when transmitted onto the line for a total of 22 bits. When the shift register is again empty,
the WBC will transfer the word in the data register to the shift register and repeat the process
if
the transmit flag is reset.
However, if the transmit flag is still set, indicating that the pro-
gram has not put a new word into the data register, the WBC will continue to put stop bits (marks)
on the line until the transmit flag is reset. When the program transfers a new word into the
data register, the transmit flag will be automatically reset and the above process will be re-
peated.
For maximum line utilization, the program must test the transmit flag and supply a
new word before the current word has been completely shifted onto the line.
1 DEF 4
2
Transmit Clock
3
Transfer Data
Register to
Transmit Buffer
4
Transmit Buffer
5
Transmit Line
6
Transmit Flag
____.n _ _ _ _ _ _
------~'--------------~
Start
i
Stop
~
0
1
1
0
1
0
1
1 0
0
1
1
1 0
0
1 0 1 1 0 1 1
Figure 21. WBC Transmit Timing Diagram
rID&1r&~~1J~ ~@------------
V-29
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