GMS81C2012/GMS81C2020
HYUNDAI MicroElectronics
(2) Noise countermeasures
In order to maintain 8-bit resolution, attention must be paid to
noise on pins AVDD and AN11 to AN0. Since the effect in-
creases in proportion to the output impedance of the analog
input source, it is recommended that a capacitor be connected
externally as shown in Figure 13-4 in order to reduce noise.
ENABLE A/D CONVERTER
A/D INPUT CHANNEL SELECT
ANALOG REFERENCE SELECT
A/D START ( ADST = 1 )
NOP
Analog
AN11~AN0
Input
100~1000pF
Figure 13-4 Analog Input Pin Connecting Capacitor
(3) Pins AN11/R73 to AN8/R70 and AN7/R67 to AN0/
R60
The analog input pins AN11 to AN0 also function as input/
output port (PORT R7 and R6) pins. When A/D conver-
sion is performed with any of pins AN11 to AN0 selected,
be sure not to execute a PORT input instruction while con-
version is in progress, as this may reduce the conversion
resolution.
ADSF = 1
YES
NO
READ ADCR
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.
Figure 13-3 A/D Converter Operation Flow
A/D Converter Cautions
(4) AVDD pin input impedance
(1) Input range of AN11 to AN0
A series resistor string of approximately 10KΩ is connected be-
The input voltage of AN11 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.
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.
64
MAR. 2000 Ver 1.00
HYNIX [ HYNIX SEMICONDUCTOR ]
