Is it possible to use ACE959-4W interface for 2 wire communication with a Sepam 40?

Goals and Symptoms

Situation
Using Modbus RS485 / 2 wire communication method for programming a Sepam 40, is it possible to use ACE959-4W interface for 2 wire communication by physically jointing A with A', and B with B' wires, and which will give the function of ACE949-2W?

Causes and Fixes

Solution
The connection of an ACE959 (designed for a 4-wires RS485 network) is quite possible on an existing 2-wires RS485 network. To do this, terminals Tx+ (B) must be jumpered to Rx+ (B') and Tx- (A) jumpered with Rx- (A') on the ACE959.

But if you are using a 2 wires RS232/RS485 convertor (ACE909-2), you must also wire, respectively :
-> the TX+RX+ (B/B') gathering wire to the L- terminal of the ACE909-2,
-> the TX-RX- (A/A') gathering wire to the L+ terminal of the ACE909-2.
(due to an inversion of polarities inside ACE959 design)

Re-published to revised security level: 17 June 2008 by DRM

Applies To: Sepam 40, ACE959

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