RS485 direction control

Embedded Devices NET+OS
1

Hi,

has anyone ever used a Connect ME to control a RS485 interface?

The problem is that I must activate the driver while the device transmits to the line and deactivate the driver as soon as the stop bit of the character sent latest has entered the line.

I did some experiments with the “Enable RTS Toggle” switch in the advanced serial settings. This seems to be very close to what I need.

However:
It works only with direct TCP connection not with the Realport (I assume the application on the PC sets handshake to NONE).

Even if I set the “Post-Delay” to 1ms it takes 3ms before the RTS line moves back to the receive state. This is far too long as even with 9600 bps some bytes of the answer are lost (with 115k it would be the complete message). The firmware did not allow me to select 0 ms (I used the web interface).

The device information of the piece I played with is:
Model: Digi Connect ME
Firmware Version: Version 82000856_E 07/01/2004
Boot Version: release_82000866_C
POST Version: release_82000867_B

Any ideas how to use the standard firmware and to avoid using an external circuit that tries to find the start bit and drive the line for exactly one bit time? Is there another firmware that does the job better?

Thanks in advance
Holger

2

Hi,

I have a similar problem: I control a RS485 driver with a GPIO. To commut the driver to reception state when emmission end I use the ‘tcdrain’ function in my custom firmware. It seemed to work well but some times this function doesn’t work and the most of the sending frame is lost… Did somebody use this function?

Paul

3

Hello,

RTS Toggle feature is broken in firmware “E” of DCME. You should use the latest firmware “F3”. It should works.

Regards,
Mikolaj