
27. Usage Notes
Rev.1.00
27.12 A/D Converter
Set registers AD0CON0 (ADST bit excluded), AD0CON1, AD0CON2, AD0CON3, and AD0CON4 while
A/D conversion stops (ADST bit is set to 0), and then set the ADST bit to 1 (A/D conversion starts.)
When the VCUT bit in the AD0CON1 register is changed from 0 (VREF not connected) to 1 (VREF
connected), wait for 1
μs or more to start A/D conversion.
Set the VCUT bit from 1 to 0 when A/D conversion is not used to reduce power consumption.
To prevent latch-up and malfunction due to noise and also to minimize a conversion error, insert capacitors
between the AVCC pin, VREF pin, analog input pin ANi_j (i = none, 0, 2, 15; j = 0 to 7), and AVSS pin. Insert
a capacitor between the VCC and VSS pins as well.
Figure 27.5 shows an example of individual pin handling.
Figure 27.5
Individual Pin Handling
Set the port direction bit in the PDk register (k = 0 to 15), which corresponds to a pin used as an analog input
pin, to 0 (input mode). When the TRG bit in the AD0CON0 register is set to 1 (external trigger) after setting
the TRG0 bit in the AD0CON2 register to 0 (ADTRG selected), set the port direction bit in the PDk register
corresponding to the ADTRG pin to 0 (input mode.)
When the key input interrupt is used, do not select pins AN_4 to AN_7 as analog input pins (key input interrupt
request is generated when the A/D input voltage becomes low (“L”.))
φAD frequency must be 16 MHz or lower. When the sample and hold is not activated, φAD frequency must be
250 kHz or higher. When the sample and hold is activated,
φAD frequency must be 1 MHz or higher.
When A/D operating mode is changed, set bits CH2 to CH0 in the AD0CON0 register or bits SCAN1 and
SCAN0 in the AD0CON1 register again to select analog input pins.
AVCC = VREF = VCC,
AD inputs (for AN_0 to AN_7, AN0_0 to AN0_7, AN2_0 to AN2_7, AN15_0 to AN15_7, ANEX0, ANEX1)
≤ VCC
VCC
VSS
AVCC
AVSS
VREF
ANi
C4
C1
C2
C3
MCU
NOTES:
1.C1
≥ 0.47
μF, C2 ≥ 0.47 μF, C3 ≥ 10000 pF, C4 ≥ 0.1 μF (reference)
2.Use thick and shortest possible wiring to connect capacitors.
VCC