At 3:57 AM -0600 3/19/03, Rowen Pereira wrote:
>I am doing a project in which i have to multiplex
>the Rx and TX lines of the serial port on to one line.
>If i do this on an 'and' gate the single line remains
>at a low (space) state.{Rx remains at mark if no data}
>I want to know what is "break" and  data is
>transmitted
>after a long "Break".
>How is this data treated.
>Is there any method you know that helps one to
>multiplex both TX and RX lines onto one line.
>Ofcourse the communication will then be half duplex
>with one comp. trxing and another Rxing at a time.
>I'll be very gratefull to get a solution.

Firstly, what does this have to do with NetBSD/Sparc?

Secondly, what you want to use is a tri-state buffer. The D(input) pin
wired to the serial port TX, the Q(output) pin wired to the serial port RX
and your communication wire, and the E(enable) pin wired to a
user-comtrolled output pin on the serial port, usually a flow control line.

When you with to transmit, set the flow control line high and send the
byte. You will then be able to read back the byte (since the RX line is
always enabled) to ensure that there were no collisions or errors. Once the
byte has left the SCC buffer you can set the flow control line back to low,
and wait for a response.

You will likely find that it is easier to just buy an few RS232<->RS485
Xcvrs, and you will also likely find it challenging designing a line
protocol that can handle arbitration, collisions, flow control and error
recovery. (unless you luck out and your SCC supports HDLC)


Cheers - Tony 'Nicoya' Mantler :)


--
Tony "Nicoya" Mantler - Renaissance Nerd Extraordinaire - nicoya@apia.dhs.org
Winnipeg, Manitoba, Canada           --           http://nicoya.feline.pp.se/