VL-1225/6 Analog Input/Output Board
4-7
Input Offset Binary Format (11-Bit Resolution)
Offset binary format is used with the bipolar ±5 or ±10V input ranges. 11-bit offset binary format divides
the full bipolar analog input range into 2048 steps. The code 0000H is associated with the most negative
voltage, i.e. –10 Volts. The largest code (07FFH) describes the most positive voltage, i.e., +9.9902 Volts.
An analog input of 0 Volts (ground) will read as 0400H. The upper five bits of the Data High register are
all zeros.
The formulas for calculating analog or offset binary digital values are given by:
Span
Digital =
———————
Analog = Step
×
(
Digital
– 1)
–
Span
Step
Where:
Analog
= Applied voltage
Digital
= A/D Conversion Data
Span
= 9.99023437
(±10V Range)
4.99511719
(±5V Range)
Step
= 0.00976563
(±10V Range)
0.00488281
(±5V Range)
Sample values are shown in the table below:
±5V Input
±10V Input
Data
Data
Voltage
Voltage
(Hex)
(Decimal)
Comment
+5.0000
+10.0000
—
—
Out of range
+4.9951
+9.9902
07FF
2047
Maximum positive voltage
+2.5000
+5.0000
0600
1536
Positive half scale
+1.2500
+2.5000
0500
1280
Positive quarter scale
+0.00488
+0.00977
0401
1025
Positive 1 LSB
0.0000
0.0000
0400
1024
Zero (ground input)
–0.00488
–0.00977
03FF
1023
Negative 1 LSB
–1.2500
–2.5000
0300
768
Negative quarter scale
–2.5000
–5.0000
0200
512
Negative half scale
–5.0000
–10.0000
0000
0
Maximum negative voltage
Figure 4-5. Offset Binary Data Format (11-Bit Resolution)
Registers – Analog Input Registers
