Setting Up Communications Hardware and Network Communications
7-37
S7-200 Programmable Controller System Manual
A5E00066097-02
If you are using the PC/PPI cable in a system where Freeport communication is
used, the turnaround time must be comprehended by the user program in the
S7-200 CPU for the following situations:
• The S7-200 CPU responds to messages transmitted by the RS-232 device.
After receiving a request message from the RS-232 device, the transmission
of a response message by the S7-200 CPU must be delayed for a period of
time greater than or equal to the turnaround time of the cable.
• The RS-232 device responds to messages transmitted from the S7-200 CPU.
After receiving a response message from the RS-232 device, the
transmission of the next request message by the S7-200 CPU must be
delayed for a period of time greater than or equal to the turnaround time of
the cable.
In both situations, the delay allows the PC/PPI cable sufficient time to switch from
transmit mode to receive mode so that data can be transmitted from the RS-485
port to the RS-232 port.
Table 7-9 PC/PPI Cable Turnaround Time (Transmit to Receive Mode)
Baud Rate
Turnaround Time (in Milliseconds)
38400 0.5
19200 1
9600 2
4800 4
2400 7
1200 14
600 28
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