VersaLogic STD32 VL-1225, Справочное руководство

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VL-1225/6 Analog Input/Output Board
4-9
Input Two’s Complement Format (11-Bit Resolution)
Two’s complement format is used with the bipolar ±5 or ±10V input ranges. 11-bit two’s complement
format, like 11-bit offset binary format, divides the full bipolar analog input range into 2048 steps. The
code 0000H, however, is associated with an analog input voltage of 0 Volts (ground). Positive analog input
voltages are represented by positive digital numbers, whereas negative analog input voltages are
represented by negative digital numbers (encoded in an 11-bit field), i.e., –1 = 07FFH. The upper five bits
of the Data High register are all zeros. Two’s complement format is the most common format for
expressing bipolar analogs.
The formulas for calculating analog or two’s complement digital values are given by:

Analog

Digital =

————

Analog = Step
×
Digital

Step

Where:
Analog = Applied voltage
Digital = A/D Conversion Data
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 03FF 1023 Maximum positive voltage
+2.5000 +5.0000 0200 512 Positive half scale
+1.2500 +2.5000 0100 256 Positive quarter scale
+0.00488 +0.00977 0001 1 Positive 1 LSB
0.0000 0.0000 0000 0 Zero (ground input)
– 0.00488 – 0.00977 07FF – 1 Negative 1 LSB
– 1.2500 – 2.5000 0700 – 256 Negative quarter scale
– 2.5000 – 5.0000 0600 – 512 Negative half scale
– 5.0000 – 10.0000 0400 – 1024 Maximum negative voltage
Figure 4-7. Two’s Complement Data Format (11-Bit Resolution)
Registers – Analog Input Registers