Hello,

I don't understand what is the echo mode in the rs232/rs485 converter. What does it mean physically?

Thanks for answering.

 

This is likely VENDOR specific, but RS-485 2-wire is half-duplex. The Receiver and Transmitter enable are independent, so WHILE YOU TRANSMIT on RS-485 2-wire, your receive (seen on RS-232) can be either enabled or disabled.

If rcv is enabled, you'll see an echo of all you send. Some CPU use this as a form of "timing control" - if you send 210 bytes, when you receive the 210th byte as echo your message has been sent completely and you can turn the RS-485 transmitter off. I suppose it also gives you a crude "collision detect" as you could compare what you sent to the echo.

If rcv is disabled, you'll NOT get an echo of what you sent. How you turn off the RS-485 transmitter off must then be handled by your lower level drivers.

Best Regards - LynnL, www.digi.com

 

An RS485 interface has a transmitter and a receiver connected in parallel to the same pair of RS485 wires. In a true RS485 interface, only one of them is operational (and the other not) at any single moment, so, for example, when the transmitter transmits, the received is "deaf". Some vendors provide a 2- or 4-wire interface (the latter is actually RS422 not RS485) and , in 2-wire mode, the choice to disable or not the receiver when the transmitter is enabled. If the receiver is not disabled in 2-wire mode, it receives every bit and character transmitted by the transmitter and presents it as echo at the RS232 interface. Meir

 

I have seen this mode when activated a full duplex device, it internally connected its transmit to its receive on the input side and all sent characters are "echoed" back to the transmitter. This was used to troubleshoot a link up to the device.

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected] (b) [email protected] (h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.