IBM nec pd78082 User Manual

In order to maintain 8-bit resolution, attention must be paid to noise on pins AV

REF

 and ANI0 to ANI7.  Since

the effect increases in proportion to the output impedance of the analog input source, it is recommended that

a capacitor be connected externally as shown in Figure 10-10 in order to reduce noise.

The analog input pins ANI0 to ANI7 also function as input/output port (PORT1) pins.  When A/D conversion

is performed with any of pins ANI0 to ANI7 selected, be sure not to execute a PORT1 input instruction while

conversion is in progress, as this may reduce the conversion resolution.

Also, if digital pulses are applied to a pin adjacent to the pin in the process of A/D conversion, the expected

A/D conversion value may not be obtainable due to coupling noise.  Therefore, avoid applying pulses to pins

adjacent to the pin undergoing A/D conversion.

A series resistor string of approximately 10 k

Ω

 is connected between the AV

REF

 pin and the AV

SS

 pin.

Therefore, if the output impedance of the reference voltage source is high, this will result in parallel connection

to the series resistor string between the AV

REF

 pin and the AV

SS

 pin, and there will be a large reference voltage

error.

ANI0-ANI7

AV

REF

V

DD

AV

DD

AV

SS

V

SS

Reference
Voltage Input

C=100-1000 pF

If there is possibility that noise whose
level is AV

REF

 or higher or AV

SS

 or lower may enter, 

clamp with a diode with a small V

F

 (0.3 V or less).

V

DD