I have an application where I send semi-duplex messages on an RS485 bus.
My slave devices on this bus are normally in receive-mode, listen for commands, and when they get a command they switch to transmit-mode and transmit a response to the master.
The slaves use the EUSART of a PIC16F1788 microcontroller.
I've noticed that the last byte in this response is sometimes corrupt.
I have a theory that this might be because the last byte of the message is not completely transmitted before the slave disables the driver on the RS485 interface chip I'm using, and thus cutting the last byte short.
My code for waiting until the transmit is done is like this:
RS485_DRIVER_ENABLE is a #define mapped to an output pin connected to the transmit enable on the RS485-chip.
Reading the PIC manual:
"The TRMT bit remains clear until all bits have been shifted out of the TSR register."
However, what I'm really interested in is that all bits actually be transmitted, so the above seems to not be exactly the right guarantee I would like.
Should I add a delay of say 2-3 bits after the TRMT is signalled?
Is there any "best practice" for this sort of thing?