Data Exchange Protocol
320 3BDS011222-510 B
Figure 192 shows the detailed view of protocol work flow.
Characteristics of the protocol is listed below:
• A protocol cycle is always initiated by PLC. It will prepare data and raise
Command bit when the state is 0.
• The PLC will not lower its Command bit until the PC has Acknowledged it (i.e.
raised the Acknowledge Bit by copying TRIGGER word to ACKNOWLEDGE
word). Otherwise it will continue to TRIGGER PC at a specified time-out
interval (formal parameter ASB_TO of DataEx1).
• Similarly PLC will not terminate an acknowledged protocol cycle until the PC
has lowered the Acknowledge Bit by copying TRIGGER word to
ACKNOWLEDGE word. Again the PLC continues to TRIGGER PC at a
specified time-out interval (formal parameter ARB_TO of DataEx1).
Figure 192. Data Exchange Protocol, Detailed Description
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