Easy to communicate between devices
7.10 PtP, USS, and Modbus communication protocols
Easy Book
166 Manual, 03/2014, A5E02486774-AF
Calculating the time required for communicating with the drive
Communications with the drive are asynchronous to the CPU scan. The CPU typically
completes several scans before one drive communications transaction is completed.
The USS_PORT interval is the time required for one drive transaction. The table below
shows the minimum USS_PORT interval for each communication baud rate. Calling the
USS_PORT function more frequently than the USS_PORT interval will not increase the
number of transactions. The drive timeout interval is the amount of time that might be taken
for a transaction, if communications errors caused 3 tries to complete the transaction. By
default, the USS protocol library automatically does up to 2 retries on each transaction.
Table 7- 14 Calculating the time requirements
Calculated minimum USS_PORT call
Interval ( milliseconds )
Drive message interval timeout per
drive ( milliseconds )
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