Hi!

I have a project in Step 7 v13  SP1 with S7-1211C CPU (6ES7211-1BE40-0XB0 v4.1) and CM 1241 (6ES7241-1CH32-0XB0 V2.1). I need to read in the 20001 - 29999 interval. The problem is that this interval appears not to be defined in standard Modbus RTU. In the Modbus_Master function help from Step7 v13 SP1 I read that if I use MODE 104 I can read registers form 0 to 65535. MODE uses FC04 for reading.

I found a recent FAQ from Siemens referring  to MODE 104, but not explicitly to 20001 - 29999.

My querstion is if someone read in 20001 - 29999 interval in this way. Unfortunately I cannot test this because I do not have access to the slave with which I am supposed to communicate until commissioning. 

Best regards,

h2_504

Hi smiffy!

The problem is that I need to read some registers in 20001-29999 area. I also am confused, about this area, because I never read something from there, as it does not appear in Modbus specification. In this area of registers the producer of the slave I am supposed to read from placed some info.

Reading the documentation for S71200 CM1241, I found that I can use MODE 104 (which uses FC04) to read from address 0 to 65535. If I use MODE104, the Modbus Master function automatically uses FC04 The question is if I can do this (if someone tried it). I cannot try it, because I do not have access to the slave.

I also can switch to CP341, to control directly the function I am about to read. But here also I am worried that if I use a specific function (FC04) and a specific address (20247) I will get errors from the compiler or the CP341 will not work in this combination. From the slave point of view, I am not worried because in the documentation it says that addresses 20001 - 29999 can be read with FC 04.

Best regards,

h2_504