Siemens SIMATIC S5 Manual page 98

Byte 22 Self-tuning parameters
If no self-tuning is required for a particular controller, all the bits in the "self-tuning"
bytes must be set to 0, otherwise bit 1 must be set.
7
Bit 2 starts and stops the self-tuning function which refers to the individual
controller. If the bit is set in the start-up OB of the user program, a configured
self-tuning function starts up when the module is switched on.
If the module has aborted a running self-tuning function, e.g. if marginal conditions
have not been met, bit 2
is set in byte 23. Byte 23 also indicates the characteristics if parameters have been
determined successfully or not.
After the voltage has returned the firmware-internal edge flag is set to 0, i.e. when
switching on or plugged in the module for the first time, it must not be set to zero
(i.e. stop) by the user before he initially starts the system.
The user can only stop the self-tuning function by means of the commands "KS"
or "SE". The system must always be stopped before a new self-tuning function is
activated.
7
Bit 2 Is only evaluated by the new FB 162 with 64 messages.
4
Bit 2 Is only evaluated by the old FB 162 with 32 messages.
IP244
C79000–B8576–C860–02
Data Exchange with the Central Controller
7
is reset and the bit with the meaning "self-tuning aborted"
4–31