
176
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (A/D Converter)
5.18 A/D Converter
5.18.1 Characteristics and
configuration of A/D converter
The S1C88409 has a built-in A/D converter with
the following characteristics.
Conversion formula: Successive-approximation
type
Resolution:
10 bits
Input channel:
Maximum 8 channels
Conversion time:
Minimum 11 sec
(in 2 MHz operation)
Setting of analog conversion voltage range is
possible with reference voltage terminal (AVREF)
A/D conversion result is possible to read from
10-bit data register
Sample & hold circuit built-in
A/D conversion completion generates an
interrupt
Figure 5.18.1.1 shows the configuration of the A/D
converter.
5.18.2 Terminal configuration
of A/D converter
The terminals used with the A/D converter are as
follows:
AVDD, AGND, AVSS
(power supply input terminal)
The AVDD, AGND and AVSS terminals are power
supply terminals for the A/D converter. The
voltage should be input as AVDD
≤ VDD and
AGND
≥ AVSS = VSS. These power supply termi-
nals are common with the D/A converter.
AVREF (reference voltage input terminal)
The AVREF terminal is the reference voltage
terminal of the analog block. Input voltage range
of the A/D conversion is decided by this input
(AGND–AVREF). The voltage should be input as
AVREF
≤ AVDD.
This terminal is used as the reference voltage input
of the D/A converter.
AD0–AD7 (analog input terminal)
The analog input terminals AD0–AD7 are shared
with the I/O port terminals P30–P37. Further, the
AD6 (P36) and AD7 (P37) terminals can be used as
the analog output terminals DA0 and DA1 of the
D/A converter. Therefore, it is necessary to set
them for the A/D converter by software when
using them as analog input terminals. This setting
can be done for each terminal. (Refer to Section
5.18.4 for setting.)
At initial reset, all the terminals are set in the I/O
port terminal.
Analog voltage value AVIN that can be input is in
the range of AVSS
≤ AGND ≤ AVIN ≤ AVREF.
10-bit
D/A converter
Data
bus
AVDD
AVREF
AGND
AVSS
Analog
multiplexer
Control circuit
AD0 (P30)
AD1 (P31)
AD2 (P32)
AD3 (P33)
AD4 (P34)
AD5 (P35)
AD6 (P36)
AD7 (P37)
Successive
conversion
register
Converted data
(ADDR)
OSC3
oscillation circuit
Prescaler
Interrupt
circuit
+
–
Sample/hold
circuit
Comparator
fOSC3
fOSC3/1 to fOSC3/16
Fig. 5.18.1.1 Configuration of A/D converter