Re: RS232 Full Duplex to Half Duplex
From: Tauno Voipio (tauno.voipio_at_iki.fi.NOSPAM.invalid)
Date: Fri, 25 Mar 2005 08:21:31 GMT
> Well I am not an expert on rs232 communication, but I was told by my
> professer that in half duplex rs232 there was only 1 wire between the
> two devices. What I am trying to do is control a device that works at
> 57600 baud rate but in Half Duplex mode. But when I was studying the
> diagrams for the device I am trying to control it has both a Tx and Rx
> wire. If anyone could point me in the direction of a good rs232 serial
> communication protocol document I would appretiate it.
That's not correct - the RS-232 standard specifies the 25 pin
connector between a DTE (Data terminal Equipment, a computer or
terminal) and a DCE (Data Communication Equipment, a modem). The
spec contains, among a lot of control lines, separate transmit
and receive lines (even another pair for reverse channel).
If your RS-232 means the common misuse meaning in fact asynchronous
serial byte-by-byte transfer, then the single data line configuration
is possible. The connection is often called a party line: all receivers
are connected directly to the line and all transmitters are connected
via enabling/disabling gates to the line. The enable logic may be
internal to the tranmit interface chip or a separate chip.
It's up to you to decide on the connection. You'll need some
kind of interface chips anyway - the RS-232 standard signal
levels are not compatible with the processor and UART signals
If the RS-232 spec is not to be taken too literally, one solution
is to use RS-485 connection and interface chips (Google for it).
Please note that you need a couple of resistors to feed the idle
state to the line when all transmitters are turned off.
-- Tauno Voipio tauno voipio (at) iki fi