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M16C/28 Group
Under development Preliminary specification
Specifications in this manual are tentative and subject to change.
15. A-D Converter
Rev.0.60 2004.02.01
page 236 of N
REJ09B0047-0060Z
Microcomputer
NOTES
1. C1
≥0.47F, C2≥0.47F, C3≥100pF, C4≥0.1F (reference)
2. Use thick and shortest possible wiring to connect capacitors.
AVCC
AVSS
VREF
ANi
C4
C1
C2
C3
VCC
VSS
ANi: ANi(i=0 to 7), AN0i (i=0 to 7 for 80-pin version, and i=0 to 3 for 64-pin version)
AN2i (i=0 to 7 for 80-pin version, i=4 for 64-pin version)
15.6 Precautions of Using A-D Converter
(1) Set the bit in the port direction register, which corresponds to the pin being used as the analog input,
to “0” (input mode) Set the bit in the port direction register, which corresponds to pin ADTRG, to “0”
(input mode) if the external trigger is used.
(2) When using a key input interrupt, do not use pins AN4 to AN7 as analog input pins (key input interrupt
request is generated when the A-D input voltage is “L”).
(3) Insert capacitors between pins AVCC, VREF, analog input pin (ANi (i=0 to 7), AN0i and AN2i) and AVSS
to prevent latch-ups and malfunctions due to noise, and to minimize conversion errors. The same
applies to pins VCC and VSS. Figure 15.6.1 shows the procedure of each pin.
(4) Incorrect values are stored in the ADi register (i=0 to 7) if the CPU reads the ADi register while the ADi
register is storing results from a completed A-D conversion. This occurs when a divided main clock or
a sub clock is selected as the CPU clock.
In one-shot mode or single sweep mode, simultaneous sample sweep mode and delayed trigger
mode 0, 1 , read the corresponding ADi register after verifying that the A-D conversion has been
completed. (The completion of the A-D conversion can be determined by the IR bit in the ADIC
register).
In repeat mode, repeat sweep mode 0 and repeat sweep mode 1, use an undivided main clock as
the CPU clock.
(5) Conversion results of the A-D converter are indeterminate, if the ADST bit in the ADCON0 register is
set to “0” (A-D conversion halted) and the conversion is forcibly terminated, by program during A-D
conversion. ADi registers not operating A-D conversion may also be indeterminate. If the ADST bit is
changed to “0” by program, during the A-D conversion, do not use any values obtained from the ADi
registers.
Figure 15.6.1 VCC, VSS, AVCC, AVSS, VREF and ANi Connections