Specifications

70
Schneider Electric
The Modbus Protocol (continued)
Program commands: Function 13
Program commands can be used to perform the following functions:
b Connect to slave memory.
b Disconnect from slave memory.
b Stop slave (STOP).
b Run slave (RUN).
b Unload program from slave (read contents of the memory).
b Load program in slave (write memory).
The functions used to load and unload the memory can also be used to read and
write the data memory in excess of the 16-bit addressing limit.
The memory load and unload commands are accessible at all times. Program
commands must be organised within a session composed of:
b Connection.
b Commands.
b Disconnection.
Note: Read and write commands cannot be mixed within a single session.
If the response is a "no acknowledgement" (exception response 7) the diagnostic
associated with these functions is obtained with function 14 (see the following
section).
Only one coupler at a time can access the slave’s memory and/or give orders to the
slave’s central processing unit.
This mutual exclusion is respected by organising program commands in sessions:
b Program commands themselves (stop, run, unload, load, etc.).
b Memory disconnection.
Notes:
b The data memory is always accessible regardless of the status of the coupler
(connected or not). Thus the principle of mutual exclusion is respected.
b An automatic disconnection procedure (time out, etc.) on the slave should be
provided in case the disconnection command does not arrive at its destination (line
out of operation, character error, etc.).
Guide to Integration
Modbus / Jbus