VersaLogic STD32 VL-1225, Справочное руководство

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4-8
VL-1225/6 Analog Input/Output Board
Input Two’s Complement Format (10-Bit Resolution)
Two’s complement format is used with the bipolar ±5 or ±10V input ranges. 10-bit two’s complement
format, like 10-bit offset binary format, divides the full bipolar analog input range into 1024 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 a 10-bit field), i.e., –1 = 03FFH. The upper six 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 = 0.01953125 (±10V Range)
0.00976563 (±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
+4.9902 +9.9805 01FF 511 Maximum positive voltage
+2.5000 +5.0000 0100 256 Positive half scale
+1.2500 +2.5000 0080 128 Positive quarter scale
+0.00977 +0.01953 0001 1 Positive 1 LSB
0.0000 0.0000 0000 0 Zero (ground input)
– 0.00977 – 0.01953 03FF – 1 Negative 1 LSB
– 1.2500 – 2.5000 0380 – 128 Negative quarter scale
– 2.5000 – 5.0000 0300 – 256 Negative half scale
– 5.0000 – 10.0000 0200 – 512 Maximum negative voltage
Figure 4-6. Two’s Complement Data Format (10-Bit Resolution)
Registers – Analog Input Registers