4518 Datasheet, PDF (76/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 Group
18 _{A/D converter-1}
• When the TALA instruction is executed, the low-order 2 bits of
register AD is transferred to the high-order 2 bits of register A, si-
multaneously, the low-order 2 bits of register A is “0.”
• Do not change the operating mode (both A/D conversion mode
and comparator mode) of A/D converter with the bit 3 of register
Q1 while the A/D converter is operating.
• Clear the bit 2 of register V2 to “0” to change the operating mode of
the A/D converter from the comparator mode to A/D conversion mode.
• The A/D conversion completion flag (ADF) may be set when the
operating mode of the A/D converter is changed from the com-
parator mode to the A/D conversion mode. Accordingly, set a
value to the register Q1, and execute the SNZAD instruction to
clear the ADF flag.
19 _{A/D converter-2}
Each analog input pin is equipped with a capacitor which is used
to compare the analog voltage. Accordingly, when the analog volt-
age is input from the circuit with high-impedance and, charge/
discharge noise is generated and the sufficient A/D accuracy may
not be obtained. Therefore, reduce the impedance or, connect a
capacitor (0.01 µF to 1 µF) to analog input pins (Figure 73).
When the overvoltage applied to the A/D conversion circuit may
occur, connect an external circuit in order to keep the voltage
within the rated range as shown the Figure 74. In addition, test
the application products sufficiently.
Sensor
AI N
LA 8
TV2A
LA 0
TQ1A
SNZAD
NOP
; (✕0✕✕2)
; The SNZAD instruction is valid ........ ➀
; (0✕✕✕2)
; Operation mode of A/D converter is
changed from comparator mode to A/D
conversion mode.
✕ : these bits are not used here.
Fig. 72 A/D converter program example-3
Apply the voltage withiin the specifications
to an analog input pin.
Fig. 73 Analog input external circuit example-1
Sensor
About 1kΩ
AIN
Fig. 74 Analog input external circuit example-2
Rev.3.01 2005.06.15 page 76 of 157
REJ03B0008-0301