Siemens SIMATIC S5 Manual page 251

Communication Between the CPU and the IP 266
The IP 266 scans this TOGGLE bit in each firmware cycle, and starts a new job
where appropriate (see Figure 7-2).
IP 266
cycle
1
Bit 7
0
Job request is interpreted in this cycle
Figure 7-2. Interpreting a Job Order in Dependence on the TOGGLE Bit
Example: Give the IP 266 the Start command for the specified mode by coding
byte 1 as shown below. Before the command was forwarded to the IP, bit 7 was 0.
Byte Bit 7 Bit 6 Bit 5
1 1 0 0
This issues the Start command "Forward" to the IP 266. The mode is started be-
cause the TOGGLE bit (bit 7) changed from 0 to 1.
7-6
Cycle trigger; beginning of a new cycle
Bit 4 Bit 3 Bit 2 Bit 1
0 0 1 0
t
Bit 0
0
EWA 4NEB 812 6057-02
IP 266