On Thu, Dec 14, 2023 at 01:41:47PM +0000, Christoph Niedermaier wrote: > I will summarize the current situation from my point of view, maybe it helps: > > RS-232: > - Full Duplex Point-to-Point connection > - No transceiver control with RTS > - No termination > - No extra struct in use > > RS-422: > - Full Duplex Point-to-Point connection > - No transceiver control with RTS needed > - Termination possible > - Extra struct serial_rs485 needed if termination is used > => RS-422 can be used in RS-232 operation, but if a termination should be > switchable the RS485 flag has to be enabled. But then also transceiver > control will be enabled. Not a very satisfying situation. Well why don't we just allow enabling or disabling RS-485 termination independently from the SER_RS485_ENABLED bit in struct serial_rs485? Just let the user issue a TIOCSRS485 ioctl to toggle termination even if in RS-232 mode and use that mode for RS-422. Looks like the simplest solution to me. > RS-485 (2-wire) very common: > - Half Duplex RS-485 bus > - Transceiver control with RTS is needed > - Termination possible > - Extra struct serial_rs485 is needed > => RS-485 has to be enabled and configured: > - Set SER_RS485_ENABLED > - Set SER_RS485_RTS_ON_SEND or SER_RS485_RTS_AFTER_SEND > - Set/clear SER_RS485_RX_DURING_TX depending on whether > the receiver path should be on or off during sending. > If it's set it allows to monitor the sending on the bus > and detect whether another bus device is transmitting > at the same time. > - Set/clear SER_RS485_TERMINATE_BUS for bus termination. > > RS-485 (4-wire) little used: > - Full Duplex RS-485 bus > - Transceiver control with RTS is needed > - Termination possible > - Extra struct serial_rs485 is needed > => RS-485 has to be enabled and configured: > - Set SER_RS485_ENABLED > - Set SER_RS485_RTS_ON_SEND or SER_RS485_RTS_AFTER_SEND > - Set SER_RS485_RX_DURING_TX, as the receiver should always > be enabled independently of TX, because TX and RX are > separated from each other by their own wires. > - Set/clear SER_RS485_TERMINATE_BUS for bus termination. Thanks for that overview, I found it very helpful. One small addendum: Hardware flow control. Only possible with RS-232. Doesn't work in any of the other modes, right? Thanks, Lukas
