Siemens Simatic S7-200 System Manual page 398

S7-200 Data Sheets
Output Data Word Format
Figure A-45 shows where the 12-bit data value is placed within the analog output word of the
CPU. Figure A-46 shows the EM235 output block diagram.
AQW XX
AQW XX
Figure A-45
Note
The 12 bits of the digital-to-analog converter (DAC) readings are left-justified in the output
data word format. The MSB is the sign bit: zero indicates a positive data word value. The
four trailing zeros are truncated before being loaded into the DAC registers. These bits
have no effect on the output signal value.
Output Block Diagram
Figure A-46 shows the EM235 output block diagram.
Vref
11
DATA
Digital-to-analog converter
Figure A-46
A-74
MSB
15 14
0 Data value
Current output data format
MSB
15
Data value
Voltage output data format
Output Data Word Format
+
-
D/A converter
+/- 2V
0
EM235 Output Block Diagram
LSB
4 3
11 Bits 0 0 0 0
LSB
4 3
12 Bits 0 0 0 0
R
-
+
Voltage-to-current converter
R
M
+
-
R
Voltage output buffer
1/4 R
M
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
0
0
+24 Volt
100
Iout
0..20 mA
Vout
-10.. +10 Volts