11
11-34
A-D Converters
32180 Group User's Manual (Rev.1.0)
11.3.2 A-D Conversion by Successive Approximation Method
The A-D Converters use an A-D conversion start trigger (software or hardware) as they start A-D conversion.
Once A-D conversion begins, the following operation is automatically performed.
1. During single mode, A-D Single Mode Register 0’s A-D conversion/comparate completion bit is cleared to "0".
During scan mode, A-D Scan Mode Register 0’s A-D conversion completion bit is cleared to "0".
2. The content of the A-D Successive Approximation Register is cleared to H’0000.
3. The A-D Successive Approximation Register’s most significant bit (bit 6) is set to "1".
4. The comparison voltage, Vref (Note 1), is fed from the D-A Converter into the comparator.
5. The comparison voltage, Vref, and the analog input voltage, VIN, are compared, with the comparison result
stored in bit 6.
If Vref < VIN, then bit 6 = "1"
If Vref > VIN, then bit 6 = "0"
6. Operations in 3 through 5 above are executed for all other bits from bit 7 to bit 15.
7. The value stored in the A-D Successive Approximation Register by the time comparison for bit 15 has finished
is held in it as the A-D conversion result.
11.3 Functional Description of A-D Converters
1st comparison
b6 7 8 9 1011121314b15
100000000
0
n910000000
0
n9n81000000
0
n9 n8 n7 n6 n5 n4 n3 n2 n1
1
2nd comparison
3rd comparison
0th comparison
Conversion
p
n9 n8 n7 n6 n5 n4 n3 n2 n1 n0
Result of 1st comparison
Result of 2nd comparison
If Vref > VIN, then nX = 0
If Vref < VIN, then nX = 1
A-D Successive Approximation Register (ADiSAR) i = 0, 1
Figure 11.3.2 Changes of the A-D Successive Approximation Register during A-D Convert Operation
Note 1: The comparison voltage, Vref (the voltage fed from the D-A Converter into the comparator), is
determined according to changes of the A-D Successive Approximation Register content. Shown
below are the equations used to calculate the comparison voltage, Vref.
• If the A-D Successive Approximation Register content = 0
Vref [V] = 0
• If the A-D Successive Approximation Register content = 1 to 1,023
Vref [V] = (reference voltage VREF / 1,024) × (A-D Successive Approximation Register content – 0.5)
To Next Page
Need help?
General
