
184
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (D/A Converter)
5.19 D/A Converter
5.19.1 Characteristics and configuration
of D/A converter
The S1C88409 has built-in two channels of D/A
converter with the following characteristics.
Conversion formula: R-2R ladder type
Resolution:
8 bits
Output channel:
2 channels
Conversion time:
Minimum 30 sec
(load capacitance: 100 pF)
Output voltage range: 0 V to AVREF
(AVREF/256 steps)
Figure 5.19.1.1 shows the configuration of the D/A
converter.
5.19.2 Terminal configuration
of D/A converter
The terminals used with the D/A 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 A/D converter.
AVREF (reference voltage input terminal)
The AVREF terminal is the reference voltage
terminal of the analog block. Output voltage range
of the D/A 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 A/D converter.
It is possible to turn AVREF on and off by software.
Refer to Section 5.18, "A/D Converter", for details.
DA0, DA1 (analog output terminal)
The analog output terminals DA0 and DA1 are
shared with the I/O port terminals P36 and P37.
Further, those terminals can be used as the analog
input terminals AD6 and AD7 of the A/D con-
verter. Therefore, it is necessary to set them for the
D/A converter by software when using them as an
analog output terminal. This setting can be done
for each terminal. (Refer to Section 5.19.4 for
setting.)
At initial reset, both the terminals are set in the
I/O port terminals.
5.19.3 Mask option
I/O port pull-up resistor
P36 (DA0)
s
s With resistor Gate direct
P37 (DA1)
s
s With resistor Gate direct
The output terminals of the D/A converter are
shared with the I/O port terminals P36 and P37.
Therefore, the terminal specification of the D/A
converter is decided by setting the I/O port mask
option. Select "Gate direct" for the port corre-
sponding to the channel to be used to obtain the
conversion precision.
8-bit
D/A converter
Data
bus
AVDD
AVREF
AGND
AVSS
DA0 (P36)/DA1 (P37)
Conversion data register
(DADR)
Control circuit
Fig. 5.19.1.1 Configuration of D/A converter