
I-90
EPSON
S1C62740 TECHNICAL HARDWARE
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (A/D Converter)
Since the slope of the reverse integral waveform is fixed, the coun-
ter value according to the integral result of the input voltage in step
(2) is obtained from the dual slope counter. The counter value n at
this time is indicated by the following expression.
0 = Vint - (-VR * n * T / CI * RI)
(Expression 4.12.2)
According to Expression 4.12.1 and Expression 4.12.2, it becomes
n = VIN * N / VR
(Expression 4.12.3)
The value of the input voltage is determined by reading and
processing this value using software.
VIN = n * VR / N
(Expression 4.12.4)
The reference voltage reverse integration period shown in Table
4.12.3 is the time for counting the full scale and, actually, the A/D
conversions is completed at the point where the output of the
integral AMP has become "0".
(4) Circuit related differences due to measurement items
The A/D conversion sequence does not differ depending on the
items selected. It responds to the respective selected items by
partially changing over the circuit.
Voltage measurement mode
For voltage measurement, the GND level is added to the non-
inverted input of the integral AMP and the specified analog input is
A/D converted as opposite the GND level.
VR2 is used for the reference voltage VR. (Calculate as VR = 163.8 mV.)
Differential voltage measurement mode
For differential voltage measurement, the input level of AI0 (for
AI1–AI0 measurement) or the input level of AI2 (for AI3–AI2 meas-
urement) is added to the non-inverted input of the integral AMP
and the specified analog input of AI1 or AI3 is respectively A/D
converted as the opposite AI0 or opposite AI2 level.
VR2 is used for the reference voltage VR. (Calculate as VR = 163.8 mV.)
Fig. 4.12.14
Circuit diagram at the
time of differential
voltage measurement
+
–
BUF
-VR
VR
VIN
GND
+
–
+
–
CAZ
CI
BF
INT
CMP
S1
RI
S2
S3
CO
AI0(AI2)
AI1(AI3)
VR = -VR2
To A/D converter
control circuit