Analog Input
40
– Reference
VSBC-8 Reference Manual
B
INARY
F
ORMAT
(0
TO
+5V
AND
0
TO
+10V O
NLY
)
The full analog input range is divided into 4096 steps. The output code (0000h) is associated
with an analog input voltage of 0 Volts (ground). All codes are considered positive.
The formulas for calculating analog or digital values are given by:
Digital =
Analog
Step
Analog = Step Digital
x
Where:
Analog = Applied voltage
Digital
= A/D Conversion Data
Step
= 0.002441406 Volts (0 to +10V Range)
0.001220703 Volts (0 to +5V Range)
Sample values are shown in the table below:
Table 22: Binary Data Format
±5V Input
Voltage
±10V Input
Voltage
Hex
Decimal
Comment
+5.000000
+10.000000
—
—
Out of range
+4.998779
+9.997559
0FFFh
4095
Maximum voltage
+2.500000
+5.000000
0800h
2048
Half scale
+1.250000
+2.500000
0400h
1024
Quarter scale
+0.001220
+0.002441
0001h
1
1 LSB
0.000000
0.000000
0000h
0
Zero (ground input)
A
NALOG
I
NPUT
C
ODE
E
XAMPLE
The following code example illustrates the procedure for reading a ±10V analog voltage from
channel 0:
OUT
0E4h,18h
;Select channel 0 and begin conversion
BUSY: IN
AL,0E2h
;Get A/D status
AND
AL,04h
;Isolate the DONE bit
JZ
BUSY
;Loop back if conversion isn’t complete
DONE: MOV
DX,00E4h
;Point to ADCLO register
IN
AX,DX
;16-bit input reads ADCLO and ADCHI into AX
