Siemens SIMATIC S5 Manual page 250

IP 266
7.1.2 Byte 1: Commands
The commands for executing a mode depend on the mode specified in byte 0.
Table 7-4 lists the permissible commands for all modes.
Command
START
STOP
FORWARD
REVERSE
TRANSFER
Note:
Only one of the bits 0 to 4 may be set at any given time. An error is flagged if
you set more than one of these bits, and the job request is not serviced. Bits 5
and 6 must always be "0".
TOGGLE bit
Bit 7 has a special function, and is used as Execute bit. A change in the value of
this bit informs the IP 266 that a new job request has been issued. In this case, the
IP 266 interprets the frame as a new job request.
The next job cannot be started until bit 7 once again changes its signal state, thus
ensuring that a given job will not be reinterpreted and restarted in every cycle.
This bit must be set to "0" in the restart OBs, thus ensuring that the first job will
always be started on a change from 0 1.
EWA 4NEB 812 6057-02
Communication Between the CPU and the IP 266
Table 7-4. Command Codes
7 6
0/1 0
0/1 0
0/1 0
0/1 0
0/1 0
5 4 3 2 1
0 0 0 0 0
0 0 0 0 1
0 0 0 1 0
0 0 1 0 0
0 1 0 0 0
0
1
0
0
0
0
7-5