![](http://datasheet.mmic.net.cn/110000/M32186F8VFP_datasheet_3496152/M32186F8VFP_1012.png)
SUMMARY OF PRECAUTIONS
Appendix 4
Appendix 4-22
32185/32186 Group Hardware Manual
Rev.1.10 REJ09B0235-0110 May 15, 07
Appendix 4.10 Notes on A/D Converter
Appendix Figure 4.10.1 Internal Equivalent Circuit of the Analog Input Part
Appendix 4.10 Notes on A/D Converter
Forcible termination during scan operation
If A/D conversion is forcibly terminated by setting the A/D conversion stop bit (ADCSTP) to "1" during scan mode
operation and the A/D data register for the channel that was in the middle of conversion is accessed for read, the
read value shows the last conversion result that had been transferred to the data register before the conversion was
forcibly terminated.
Modification of the A/D converter related registers
If the content of any register—A/D Conversion Interrupt Control Register, Single or Scan Mode Registers or A/D
Successive Approximation Register, except the A/D conversion stop bit—is modified in the middle of A/D conver-
sion, the conversion result cannot be guaranteed. Therefore, do not modify the contents of these registers while A/D
conversion is in progress, or be sure to restart A/D conversion if register contents have been modified.
Handling of analog input signals
When using the A/D Converter with its sample-and-hold function disabled, make sure the analog input level is fixed
during A/D conversion.
A/D conversion completed bit read timing
To read the A/D conversion completed bit (the Single Mode Register 0 ADSCMP bit or the Scan Mode Register 0
ADCCMP bit), as well as the A/D simultaneous sampling status bit (the A/D0 Single Mode Register 2 ADSH2ST
bit) immediately after A/D conversion has started or has been terminated by the A/D conversion stop bit, be sure
to adjust the timing 6 BCLK periods by performing a dummy read of their registers before read.
Regarding the analog input pins
Appendix Figure 4.10.1 shows the internal equivalent circuit of the A/D Converter’s analog input part. To obtain
accurate A/D conversion results, make sure the internal capacitor C2 of the A/D conversion circuit is charged up
within a predetermined time (sampling time). To meet this sampling time requirement, it is recommended that a
stabilizing capacitor C1 be connected external to the chip.
The method for determining the necessary value of this external stabilizing capacitor with respect to the output
impedance of an analog output device is described below. Also, an explanation is made of the case where the
output impedance of an analog output device is low and the external stabilizing capacitor C1 is unnecessary.
Rated value of the absolute accuracy
The rated value of the absolute accuracy is the actual performance value of the microcomputer alone, with influ-
ences of the power supply wiring and noise on the board not taken into account. When designing the application
system, use caution for the board layout by, for example, separating the analog circuit power supply and ground
(AVCC, AVSS and VREF) from those of the digital circuit and incorporating measures to prevent the analog input
pins from being affected by noise, etc. from other digital signals.
Comparator
Inside the microcomputer
10-bit A/D Successive
Approximation Register (ADiSAR)
10-bit D/A Converter
VREF0
V2
C2
Cin : input pin capacitance (approx. 10 pF)
R2 : parasitic resistance of the
selector (1-2 K
)
C2 : comparator capacitance
(approx. 2.9 pF)
Selector
R2
i
i1
i2
→
AD0INn
→
C1
E
R1
↓
C1 : parasitic capacitance of the board
+ stabilizing capacitance
R1 : resistance of analog output device
Analog output device
Cin
E : voltage of analog output device
V2 : voltage across C2
VREF0 : analog reference voltage