can any one explain about com_modmast block for modbus rtu communication???
1.what is the function of data parameter in the block and how it works ? how to set the address?
2. how to write and read variables ? base on function it works but i want read n number of bits then how the program likes?
3. how to assign address for the values from slave ?
4. any one have backup please share ...regarding that rtu communication
1. Data parameter is the "address pointer" to which Modbus registers are being stored. In SIMATIC S7 lingo this is the Datablock pointer. Typically this is assigned by the operator ADR(datablock), where datablock can be type ARRAY[0..100] of WORD or similiar.
2. You may use function codes 1,2,3,4 for reading and 5,6,15,16 for writing. NB is the number of registers/bits to read. I would highly recommend that you read up on Modbus protocol first -> http://en.wikipedia.org/wiki/Modbus
3. Data are stored in the datablock assigned by your address pointer, in sequential order.
4. Almost every imaginable examples can be found here: http://www.abb.com/abblibrary/downloa...