MVP 2014 Simon Posted February 25, 2019 MVP 2014 Report Share Posted February 25, 2019 In helping a customer integrate a UniStream into a SCADA system I have come across a curious gap in the available information. I can't see any declaration of the function codes that the external Modbus master must use to communicate with the UniStream as a slave. The Unitronics example and tutorials use a UniStream as the master as well as the slave, which doesn't highlight this issue. I have looked within UniLogic, tried exporting the Modbus registers as excel, looked at the UniLogic help file, watched the Unitronics YouTube video and searched the forum. None of these sources gave the necessary information So far I have gleaned that the following codes are supported on a UniStream modbus slave: Coils Read Coils (function code 1) Write Coils (function code 5) Write Multiple Coils (function code 15) Registers/Words Read Holding Registers (function code 3) Write Single Register (function code 6) Write Multiple Registers (function code 16) But what if the customer's master only supports Read Input Registers (function code 4)? I don't have a firm answer on how we could handle this. Can anyone provide a definitive list? I would like to be able to answer this question with confidence. A standard part of documenting a Modbus Slave is to specify which function codes it supports, so the master can be correctly programmed. Thanks, Simon Quote Link to comment Share on other sites More sharing options...
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