Siemens SIMATIC S5 Manual page 313

IP 266
"External start enable" switch
The "External start enable" switch must be wired as an NC contact. The IP 266 will
accept no jobs until it receives a "1" signal. In FB 26, this signal is scanned and
routed via Q 2.0 to pin 7 on the IP 266's terminal block.
Selecting the functions for the different modes via IB 3
Not all functions are allowed in all modes. To preclude errors due to selection of
an invalid function, the program in FB 26 checks the function for validity. If the
RLO is 1 (valid function), the program branches to the relevant "Command FB".
Function
START
STOP
FWD/REV
TRANSFER
The table above lists only the modes programmed in the sample program.
Refer to Table 6-3 in Section 6.6.2 for a list of all modes and their functions.
EWA 4NEB 812 6057-02
Command FB For mode
FB 21 5, 6, 8, 9
FB 22 All modes
FB 23
FB 24
STEP 5 Programming
2
2, 9
9-25