Modbus Function Code 1 with Premium ETY_Ports, TSXETY4103 and 5103



Goals and Symptoms

To inform users of the reason for not being able to read 2000 Coils from a Premium ETY_Port, ETY4103 or 5103

Facts and Changes

Users attempting to read a large number of coils(1000+) from a Premium PLC through an ETY_Port, ETY4103 or 5103 will encounter an Exception Response 2 ( Illegal Data Address).

Causes and Fixes

This limitation is due to the fact that on Premium the Modbus requests are mapped on UNITE requests on the back plane. These UNITE request access the the data as Booleans. As each Boolean in Premium takes several bits (one for the value, one to indicate if it is forced or not, ....) and as UNITE requests are limited in term of size, this leads to the limitation of 1072 bits.