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How to restore the RS-485 communications on a 'Tesys U' connected to a Tesysport..

Goals and Symptoms

How to restore the RS-485 communications on a 'Tesys U' connected to a Tesysport.

Facts and Changes

TESYS U

Causes and Fixes


If '140NOE77111 'communications to the Tesysport is recovered after a lockup, the RS-485 connection to
the 'Tesys U' does not get restored. When this happens, the ERR led on the 'Tesys U' will be flashing.

In order to re-establish the RS-485 Modbus communications to the 'Tesys U', the recovery bit (bit 3 of
word 703) must be reset.

The following is from page 58 of the 'TeSys® U LULC032-033 Modbus Communication Module
Users Manual'.

Recovery After Loss of Communication
After acknowledgment by setting bit 703.3 to 1, recovery occurs according to the states of control

bits 704.0 and 704.1.

To resolve the issue the application needs to be modified to

  • Detect a 'Loss of communications with a master warning' using word 109 bit 15 as described on page
58 of the user manual.
  • Set bit 3 of word 703 upon detection of the communications loss.
  • Reset bit 3 of 703 after the 'Loss of communications with a master warning' is cleared.
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