Digital Representation Ofanalog Values - Siemens SIMATIC S5 1P 243 Equipment Manual

Function Description
3.4.2.3 Digital Representation of Analog Values
Two bytes are required for representing the values, the output from DAC1 and DAC2, in digital
form.
HIGH byte
The representation of the digital values in the bit pattern is to be interpreted in a way that the output
voltage range *1 O V is only considered as a positive range within O V to +20 V.
The 12th bit is cutoff and written separately as sign bit at position 2
value FFF , at a resolution of 12 bits, corresponds to the maximum voltage +20 V, but it is adapted
H
to the output voltage range and is converted to the negative voltage –10 V.
The digital representation of analog values over the entire rated output range appears as follows:
Units output
voltage
SN X X X X 2 '~ ~ ~ 272 !2 % ? 232
+2047 0 Xxxx o 0 0 0 0 0 0 0 0 0 0
+2000 +9.7656
0 Xxxx o 0 0 0 0 1 0 1 1 1 1
+1000 +4.8828 0 Xxxx 1 0 0 0 0 0 1 0 1 1 1
0 Xxxx 1 1 1 1 1 1 1
o o 0 Xxxx 1 1 1 1 1 1 1
-1 -0.0049 1 Xxxx o 0 0 0 0 0 0 0 0 0 0
–1000 –4.8828 1 Xxxx o 1 1 1 1 1 0 0 1 1 1
–2000 –9.7656 1 Xxxx 1 1 1 1 1 0 0 1 1 1 1
–2048 –10.0000 1 Xxxx 1 1 1 1 1 1 1
Attention: If a value provided in the two's complement form by the programmable
controller is output as an analog value, this value must first be converted
to a format suitable for a DAC1 or DAC2. For this purpose the sign bit 215
must at first be saved, then the bit pattern must be inverted (command
Attention: When the power supply of the programmable controller is initially turned
on, or when the voltage returns after power–off, DAC1 and DAC2 are pre-
set with the value 000000000000 = +9.9951. This value remains until it
3 – 8
HIGH Byte LOW Byte
1 1 1 0
1 1 1 1
1 1 1 1
LOW byte
X: irrelevant
Module address +1
Module address +3
1
5. The highest representable
Amount of
Output voltage in
bit pattern reference to range
(including
o v to +20 v
sign)
2 0
o
0.0049
0.2344
47
5.1172
1047
9.9951
2046
2047 10.0000
10.0049
2048
14.8628
3047
19.7656
4047
20.0000
4095
AG 1989, Order No: 6ES5 998-0KF21
R 02/92