Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 134)

Handshaking
Chapter 5
5Ć5
Figure 4.2
Write Handshaking
The Ladder Program Data Transfer The Module
Toggles bit CW1(16) and transfers its new
status with data to the module
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CW1(16) and new data
Detects that CW1(16) has been toggled
Moves data to output buffer where it is sent to
the ASCII device
Toggles SW1(16) and returns new status to
acknowledge receipt
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SW1(16)
Repeats the cycle when it detects a change in
SW1(16), and when you enable the oneĆshot
NOTE: The processor can write data to the module but the module will not process the data to its output buffer (inhibits data to the ASCII
device) until the module detects that your program has toggled SW1(16).
Table 5.B
Logic Conditions for a Write
If Then
SW1(16) = CW1(16) at
processor
Module has acknowledged processing the
previous block of data
Program sets CW1(16) = SW1(16) when you
enable the oneĆshot to write new data
CW1(16) ≠ SW1(16) at
module
Module moves new data to output buffer (to
ASCII device)
Module sets SW1(16) ≠ CW(16) to acknowledge
that it processed the data