Calculating The Time Required For Communicating With The Drive - Siemens Simatic S7-200 System Manual

Calculating the Time Required for Communicating with the Drive

Communications with the drive are asynchronous to the S7-200 scan. The S7-200 typically completes
several scans before one drive communications transaction is completed. The following factors help
determine the amount of time required: the number of drives present, the baud rate, and the scan time of
the S7-200.
Some drives require longer delays when using
the parameter access instructions. The amount
of time required for a parameter access is
dependent on the drive type and the parameter
being accessed.
After a USS_INIT instruction assigns Port 0 to
use the USS Protocol, the S7-200 regularly
polls all active drives at the intervals shown in
Table 11-1. You must set the time-out
parameter of each drive to allow for this task.
Tip
Only one USS_RPM_x or USS_WPM_x instruction can be active at a time. The Done output of each
instruction should signal completion before user logic initiates a new instruction.
Use only one USS_CTRL instruction for each drive.
Using the USS Protocol Library to Control a MicroMaster Drive
Table 11-1 Communications Times
Baud Time Between Polls of Active Drives
Rate (with No Parameter Access Instructions Active)
1200 240 ms (maximum) times the number of drives
2400 130 ms (maximum) times the number of drives
4800 75 ms (maximum) times the number of drives
9600 50 ms (maximum) times the number of drives
19200 35 ms (maximum) times the number of drives
38400 30 ms (maximum) times the number of drives
57600 25 ms (maximum) times the number of drives
115200 25 ms (maximum) times the number of drives
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