MC80F0224 Datasheet, PDF (73/128 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

Preliminary
MC80F0208/16/24
15. ANALOG TO DIGITAL CONVERTER
The analog-to-digital converter (A/D) allows conversion of an
analog input signal to a corresponding 10-bit digital value. The A/
D module has sixteen analog inputs, which are multiplexed into
one sample and hold. The output of the sample and hold is the in-
put into the converter, which generates the result via successive
approximation. The analog supply voltage is connected to AV_DD
of Sample & Hold logic of A/D module. The AV_DD was separat-
ed with V_DD in order to minimize the degradation of operation
characteristic by power supply noise.
The A/D module has three registers which are the control register
ADCM and A/D result register ADCRH and ADCRL. The AD-
CRH[7:6] is used as ADC clock source selection bits too. The
register ADCM, shown in Figure 15-4, controls the operation of
the A/D converter module. The port pins can be configured as an-
alog inputs or digital I/O.
It is selected for the corresponding channel to be converted by
setting ADS[3:0]. The A/D port is set to analog input port by
ADEN and ADS[3:0] regardless of port I/O direction register.
The port unselected by ADS[3:0] operates as normal port.
ADCRH and ADCRL contains the results of the A/D conversion.
When the conversion is completed, the result is loaded into the
ADCRH and ADCRL, the A/D conversion status bit ADSF is set
to “1”, and the A/D interrupt flag ADCIF is set. See Figure 15-1
for operation flow.
The block diagram of the A/D module is shown in Figure 15-3.
The A/D status bit ADSF is set automatically when A/D conver-
sion is completed, cleared when A/D conversion is in process.
The conversion time takes 7 times of conversion source clock.
The period of actual A/D conversion clock should be minimally
1µs
Analog
Input
0~1000pF
User Selectable
AN0~AN7
Enable A/D Converter
A/D Input Channel Select
Conversion Source Clock Select
A/D Start (ADST = 1)
NOP
ADSF = 1
NO
YES
Read ADCR
Figure 15-1 A/D Converter Operation Flow
How to Use A/D Converter
The processing of conversion is start when the start bit ADST is
set to “1”. After one cycle, it is cleared by hardware. The register
Figure 15-2 Analog Input Pin Connecting Capacitor
A/D Converter Cautions
(1) Input range of AN0 to AN7
The input voltage of AN0 to AN7 should be within the specifica-
tion range. In particular, if a voltage above AV_DD or below AV_SS
is input (even if within the absolute maximum rating range), the
conversion value for that channel can not be indeterminate. The
conversion values of the other channels may also be affected.
(2) Noise countermeasures
In order to maintain 10-bit resolution, attention must be paid to
noise on pins AV_DD and AN0 to AN7. Since the effect increases
in proportion to the output impedance of the analog input source,
it is recommended in some cases that a capacitor be connected ex-
ternally as shown in Figure 15-2 in order to reduce noise. The ca-
pacitance is user-selectable and appropriately determined
according to the target system.
(3) Pins AN0/R60 to AN7/R67
The analog input pins AN0 to AN7 also function as input/output
port (PORT R6) pins. When A/D conversion is performed with
any of pins AN0 to AN15 selected, be sure not to execute a PORT
input instruction while conversion is in progress, as this may re-
duce 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 ap-
plying pulses to pins adjacent to the pin undergoing A/D conver-
sion.
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