I'm trying to implement a UART on a dsPIC33E microcontroller to communicate with an industrial controller (cRIO by National Instruments) over RS485 (2-wire, half-duplex).
What I want to know is should I implement a delay before the first start bit and the last stop bit of the whole message? If yes, is there any recommendation (standard) how "long" this delay should be?
Here is a waveform of a message recorded at a serial port of the industrial controller:
For easier referencing, let's say that the far left vertical line denotes t=0 ms, whereas time division is set to 1 ms. Since the serial port is configured in a half-duplex mode, data direction can be either transmit or receive. At t=1 ms it can be seen that the port is set to the transmit mode, and at t=7.2 ms it releases the data bus, i.e., it is set to the receive mode. However, I'm concerned about these delays before the first start bit and the last stop bit. Should I also implement these delays on my microcontroller? Is this defined by any standard - hardware or software standard?
Thank you in advance!