Siemens SIMATIC CP 340 User Manual page 60

Basic Principles of Serial Data Transmission
2.6 Data transmission with the printer driver
BUSY signal
The CP 340 evaluates the printer's "BUSY" control signal. The printer indicates to the CP
340 that it is ready to receive:
● CP 340-20mA-TTY: current on RxD line
● CP 340–RS 232C and CP 340-RS 422/485: CTS signal = "ON".
Note
When RTS/CTS flow control is parameterized, you must set the polarity of the BUSY
signal on the printer as follows:
 BUSY signal: CTS = "OFF"
Please note that some printers use the DTR signal to display the BUSY signal. In such
cases you must wire the cable to the CP 340 appropriately.
60
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03