GMS81C2112 Datasheet, PDF (64/107 Pages) Hynix Semiconductor – HYNIX SEMICONDUCTOR 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS81C2112/GMS81C2120
ENABLE A/D CONVERTER
A/D INPUT CHANNEL SELECT
ANALOG REFERENCE SELECT
(2) Noise countermeasures
In order to maintain 8-bit resolution, attention must be paid to
noise on pins AVDD and AN7 to AN0. Since the effect increas-
es in proportion to the output impedance of the analog in-
put source, it is recommended that a capacitor be connected
externally as shown in Figure 13-4 in order to reduce noise.
Analog
Input
100~1000pF
AN11~AN0
A/D START ( ADST = 1 )
NOP
ADSF = 1
NO
YES
READ ADCR
Figure 13-3 A/D Converter Operation Flow
A/D Converter Cautions
(1) Input range of AN7 to AN0
The input voltage of AN7 to AN0 should be within the
specification range. In particular, if a voltage above AVDD
or below AVSS is input (even if within the absolute maximum
rating range), the conversion value for that channel can not be in-
determinate. The conversion values of the other channels may
also be affected.
Figure 13-4 Analog Input Pin Connecting Capacitor
(3) Pins AN7/R67 to AN0/R60
The analog input pins AN7 to AN0 also function as input/
output port (PORT R6) pins. When A/D conversion is per-
formed with any of pins AN7 to AN0 selected, be sure not
to execute a PORT 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.
(4) AVDD pin input impedance
A series resistor string of approximately 10KΩ is connected be-
tween the AVDD pin and the AVSS 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 AVDD pin and the AVSS pin,
and there will be a large reference voltage error.
58
JUNE. 2001 Ver 1.00