Siemens CP 243-2 - Manual (Page 62)

Access to the Data of the AS-i Slaves
3-14
SIMATIC NET CP 243-2 AS-i Master
C79000-G8976-C142/02
Representation of the Analog Values
The analog values must be interpreted complying with slave profile 7.3 or 7.4 as
16-bit values in two’s complement.
For further information about the range of values, measuring range, accuracy etc.,
refer to the relevant documentation of the analog slaves.
Special Situations
In the input direction, the CP 243-2 supplies the value 7FFF
H
when,
S
the AS-i slave does not exist, has failed, or is not an analog slave complying
with profile 7.3 or 7.4;
S
the channel number is not supported by the slave;
S
The slave signals “Value Invalid”.
In the input direction, the CP 243-2 supplies the value 0000
H
when the AS-i slave
supplies transparent data complying with profile 7.3 (extended ID2 code, bit 2=1)
and when
S
this slave has failed
S
this slave signals “Value Invalid”.
In the output direction, the CP 243-2 behaves as follows:
In the STOP mode of the PLC (more exactly: bit PLC_RUN = 0), the CP 243-2
stops transfer of the analog values. The reaction of the analog slave depends on
the particular manufacturer.
When the CP 243-2 starts up, all analog values have the default 7FFF
H
. This value
is, however, only sent after the bit PLC_RUN changes from “0” to “1”.
!
Caution
To ensure the consistency of the analog values, the CP 243-2 does not update the
analog input and analog output values as long as the bank select bit BS5 = 1.
Immediately after a read or write access to the analog values it is best to set all
bank select bits to “0”.