I want to write and receive data from a frequency response analyser. I am connecting to the instrument using a serial connection via a Serial-USB adapter. The manual says it will only transmit when CTS (pin8) is high, and only receive when DCD (pin1) is high, both are listed as input pins. Does anyone know if there is a way to send high signals to these pins when i want to transmit/receive using pySerial?
Thanks.
Today, connecting a PC to a device through a serial port is often done in a peer-to-peer relationship.
In that case, a cable called a cross cable is used to connect the two, but there is no standard specification for the pin assignment, and there are many variations.
DCD (and RI) is an input signal on both the PC and the device, and there is no corresponding output signal, so the RTS or DTR signal should be used as an alternative.
How you can handle them in software depends on the connection specifications of the cable hardware you choose.
After confirming that the RTS/DTR signal on the PC side is connected to the CTS/DCD pin on the device side of the cable, by setting rts and dtr of PySerial to True by software, the CTS/DCD on the device side turns on.

In response to comment:
If you fix the signal on the device side as described in the comment and the device side can operates in that state, the PC side will be able to send and receive at any time without additional control processing.
Setting RS232 pins using python serial