Rs232 - Siemens Simatic S7 Series System Manual

Communication

8.7 RS232

If you are using the RS232/PPI Multi-Master cable in a system where Freeport
communications is used, the program in the S7-200 SMART CPU must comprehend the
turnaround time for the following situations:
● The CPU responds to messages transmitted by the RS232 device.
After the CPU receives a request message from the RS232 device, the CPU must delay
the transmission of a response message for a period of time greater than or equal to the
turnaround time of the cable.
● The RS232 device responds to messages transmitted from the CPU.
After the CPU receives a response message from the RS232 device, the CPU must delay
the transmission of the next request message for a period of time greater than or equal to
the turnaround time of the cable.
In both situations, the delay allows the RS232/PPI Multi-Master cable sufficient time to
switch from Transmit mode to Receive mode so that data can be transmitted from the RS485
port to the RS232 port.
8.7 RS232
An RS232 network is a point-to-point connection between two devices. RS232 allows for
data transfer at relatively slow speeds (up to 115.2 kbaud) and short distances (up to 50
feet).
Possible RS232 connections include the following:
● Freeport
● Modems
● RS232-compatible devices (for example, a bar code scanner)
● Devices that have RS232 interfaces (for example, a control system)
● RS232 displays
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System Manual, 09/2015, A5E03822230-AC
S7-200 SMART