4502 Datasheet, PDF (50/116 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4502 Group
16 _{Notes for the use of A/D conversion 1}
Note the following when using the analog input pins also for
ports P2 and P3 functions:
• Selection of analog input pins
Even when P20/AIN0, P21/AIN1, P30/AIN2, P31/AIN3 are set to
pins for analog input, they continue to function as ports P2 and
P3 input/output. Accordingly, when any of them are used as I/O
port and others are used as analog input pins, make sure to set
the outputs of pins that are set for analog input to “1.” Also, the
port input function of the pin functions as an analog input is un-
defined.
• TALA instruction
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.”
17 _{Notes for the use of A/D conversion 2}
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.
When the operating mode of A/D converter is changed from the
comparator mode to A/D conversion mode with the bit 3 of regis-
ter Q1, note the following;
• Clear the bit 2 of register V2 to “0” (refer to Figure 52➀) to
change the operating mode of the A/D converter from the com-
parator mode to A/D conversion mode with the bit 3 of register
Q1.
• 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 bit 3 of register Q1, and execute the SNZAD instruc-
tion to clear the ADF flag.
18 _{Notes for the use of A/D conversion 3}
Each analog input pin is equipped with a capacitor which is used
to compare the analog voltage. Accordingly, when the analog
voltage 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, con-
nect a capacitor (0.01 µF to 1 µF) to analog input pins (Figure 53).
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 54. In addition, test
the application products sufficiently.
Sensor
AIN
Apply the voltage withiin the specifications
to an analog input pin.
Fig. 53 Analog input external circuit example-1
Sensor
About 1kΩ
AIN
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. 54 Analog input external circuit example-2
Fig. 52 A/D conversion interrupt program example
Rev.3.01 2005.02.02 page 50 of 112
REJ03B0105-0301