Siemens SIMATIC S5 Manual page 99

Data Exchange with the Central Controller
As long as the bit 2
channel is determined every time the control system is heated up.
Byte 23 Self-tuning: heating-cooling parameters
If the heating parameters calculated by the self-tuning function are available for
the controller, bit 4 is set and if cooling parameters are present, bit 0 is set.
Assignment of bits to the controllers:
Once the self-tuning function has calculated the parameters for heating, bit 4 in
byte 23 is set for each controller. If the self-tuning function is reactivated, the bit
is cleared. This can be checked simply with FB 162 using the "LE" command. The
same applies to bit 0 for cooling with 3-step controllers. This allows you to check
whether the parameters calculated by the self-tuning function exist or not.
If the self-tuning function of a 3-step controller has calculated heating parameters
but no cooling parameters, the system deviation-temperature jump is not high
enough. In byte 30 of messages 0 to 12 you can see how high the temperature
jump must be to allow the self-tuning function to calculate parameters for cooling.
Another possible reason is that the actual temperature value has fallen by more
than 60 C/min while simultaneously heating and cooling.
Bit 7 is set if the self-tuning function was aborted externally or internally from the
module and if no parameters or incomplete parameters were determined.
If, after the parameters have been determined, the actual value is greater than the
setpoint value and the heating is still in operation, the self-tuning function is
automatically aborted.
If no parameters can be calculated, the IP 244 continues to operate with the values
which existed before the self-tuning function was activated.
4–32
7
is set, a new parameter set for the respective controller
IP244
C79000–B8576–C860–02