GMS81C5108 Datasheet, PDF (62/102 Pages) Hynix Semiconductor – HYNIX SEMICONDUCTOR INC. 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS81C5108
ENABLE A/D CONVERTER
A/D INPUT CHANNEL SELECT
ANALOG REFERENCE SELECT
A/D START (ADST = 1)
NOP
NO
ADF = 1
YES
READ ADDR
Figure 14-2 A/D Converter Operation Flow
A/D Converter Cautions
(1) Input range of AN0 to AN3
The input voltages of AN0 to AN3 should be within the
specification range. In particular, if a voltage above AV_DD
or below V_SS is input (even if within the absolute maxi-
mum rating range), the conversion value for that channel
can not be indeterminated. The conversion values of the
other channels may also be affected.
(2) Noise countermeasures
In order to maintain 8-bit resolution, attention must be paid
to noise on pins AV_DD and AN0 to AN3. Since the effect
increases in proportion to the output impedance of the an-
alog input source, it is recommended that a capacitor is
connected externally as shown below in order to reduce
noise.
Analog
Input
100~1000pF
AN0~AN3
Figure 14-3 Analog Input Pin Connecting Capacitor
(3) Pins AN0/R20 to AN3/R23
The analog input pins AN0 to AN3 also function as input/
output port (PORT R2) pins. When A/D conversion is per-
formed with any of pins AN0 to AN3 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) AV_DD pin input impedance
A series resistor string of approximately 10KΩ is connect-
ed between the AV_DD pin and the V_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_DD pin and the V_SS
pin, and there will be a large reference voltage error.
JUNE 2001 Ver 1.0
59