UPD784938 Datasheet, PDF (424/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 16 A/D CONVERTER
Figure 16-15. Example of Capacitor Connection on A/D Converter Pins
Analog
input
100 to
500 pF
Reference
voltage input
µPD784938
ANI0 to ANI7
AVREF1
AVSS
(4) When the STOP mode or IDLE mode is used, the consumption current should be reduced by clearing (to 0) the CS
bit before entering the STOP or IDLE mode. If the CS bit remains set (to 1), the conversion operation will be stopped
by entering the STOP or IDLE mode, but the power supply to the voltage comparator will not be stopped, and therefore
the A/D converter consumption current will not be reduced.
(5) Once the A/D converter starts operating, conversion operations are performed repeatedly until the CS bit of the A/D
converter mode (ADM) is cleared (to 0). Therefore, a superfluous interrupt may be generated if ADM setting is performed
after interrupt-related registers, etc., are set when A/D converter mode conversion, etc., is performed. The result of
this superfluous interrupt is that the conversion result storage address appears to have been shifted when the scan
mode is used. Also, when the select mode is used, the first conversion result appears to have been an abnormal value,
such as the conversion result for the other channel. It is therefore recommended that A/D converter mode conversion
be carried out using the following procedure.
<1> Write to the ADM (CS bit must be set (to 1))
<2> Interrupt request flag (ADIF) clearance (to 0)
<3> Interrupt mask flag or interrupt service mode flag setting
Operations <1> to <3> should not be divided by an interrupt or macro service. When scan mode 0 (no delay control)
is used, in particular, you should ensure that the time between <1> and <2> is less than the time taken by one A/D
conversion operation.
Alternatively, the following procedure is recommended.
<1> Stop the A/D conversion operation by clearing (to 0) the CS bit of the ADM.
<2> Interrupt request flag (ADIF) clearance (to 0).
<3> Interrupt mask flag or interrupt service mode flag setting
<4> Write to the ADM
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Preliminary User’s Manual U13987EJ1V0UM00