NEC PD78F9488 - Manual (Page 185)

CHAPTER 10 10-BIT A/D CONVERTER
User’s Manual U15331EJ4V1UD
185
(9) Interrupt request flag (ADIF0)
Changing the contents of A/D converter mode register 0 (ADML0) does not clear the interrupt request flag
(ADIF0).
If the analog input pins are changed during A/D conversion, therefore, the A/D conversion result and the
conversion end interrupt request flag may reflect the previous analog input immediately before rewriting
ADML0. In this case, ADIF0 may already be set if it is read-accessed immediately after ADML0 is rewritten,
even when A/D conversion has not been completed for the new analog input.
In addition, when A/D conversion is restarted, ADIF0 must be cleared beforehand.
Figure 10-11. A/D Conversion End Interrupt Request Generation Timing
A/D conversion
ADCRL0
INTAD0
Rewriting ADML0
(to begin conversion
for ANIn) Rewriting ADML0
(to begin conversion
for ANIm)
ADIF0 has been set, but conversion
for ANIm has not been completed.
ANIn ANIn ANIm ANIm
ANIn ANIn ANIm ANIm
Remarks 1. n = 0 to 7
2. m = 0 to 7
(10) AV
DD
pin
The AV
DD
pin is used to supply power to the analog circuit. It is also used to supply power to the ANI0 to
ANI7 input circuit.
If your application is designed to be changed to backup power, the AV
DD
pin must be supplied with the same
voltage level as the V
DD
pin, as shown in Figure 10-12.
Figure 10-12. AV
DD
Pin Handling
Main power
supply Backup
capacitor
V DD
AV
DD
V SS
AV SS
(11) AV
DD
pin input impedance
A series resistor string of several ten of k Ω is connected between the AV
DD
and AV
SS
pins. Consequently, if
the output impedance of the reference voltage supply is high, the reference voltage supply will form a series
connection with the series resistor string, creating a large reference voltage differential.