Access Procedure - WAGO -I/O-SYSTEM 750 Series Manual

30 • 750-655 [AS-Interface master module]
Process image
2.1.1.7.4.2

Access procedure

The user first writes the request parameter and then the opcode and toggle
flag. As soon as the opcode or toggle flag changes, the master interprets the
mailbox range of the module bus output data as a complete mailbox command
and executes it. In doing so, the response parameters are stored in the mailbox
range of the internal bus input data.
When the command has been processed, the master mirrors the opcode and the
toggle flag. From this, the user recognizes that his request has been dealt with
and the result is available in the internal bus input data.
The toggle flag is required so that two mailbox commands with the same
opcode (but possibly different parameters) can be executed directly after one
another.
The execution of a mailbox command is declined if the number of request
parameter bytes transmitted (in the output data direction) is too small, i.e. if
the mailbox length has been set too low.
WAGO-I/O-SYSTEM 750
I/O Modules