80C196MH Datasheet, PDF (34/41 Pages) Intel Corporation – 8XC196MH INDUSTRIAL MOTOR CONTROL CHMOS MICROCONTROLLER

8XC196MH INDUSTRIAL MOTOR CONTROL CHMOS MICROCONTROLLER
®
A/D SAMPLE AND CONVERSION TIMES
Two parameters, sample time and conversion time,
control the time required for an A/D conversion. The
sample time is the length of time that the analog input
voltage is actually connected to the sample capacitor.
If this time is too short, the sample capacitor will not
charge completely. If the sample time is too long, the
input voltage may change and cause conversion
errors. The conversion time is the length of time
required to convert the analog input voltage stored on
the sample capacitor to a digital value. The
conversion time must be long enough for the
comparator and circuitry to settle and resolve the
voltage. Excessively long conversion times allow the
sample capacitor to discharge, degrading accuracy.
The AD_TIME register programs the A/D sample and
conversion times. Use the T_SAM and T_CONV specifica-
tions in Tables 16 and 18 to determine appropriate
values for SAM and CONV; otherwise, erroneous
conversion results may occur.
Use the following formulas to determine the SAM and
CONV values:
SAM = -^T---^S---^A---^M-----^×----^F----^O---^S---^C-----–----²--
8
CONV = ^T----^C---^O---^N----^V----^×-----^F---^O---^S---^C-----–----³-- – 1
2×B
where:
SAM = 1 to 7
CONV = 2 to 31
T_SAM is the sample time, in µsec
(Tables 16 and 18)
T_CONV is the conversion time, in µsec
(Tables 16 and 18)
F_OSC is the XTAL1 frequency, in MHz
B is the number of bits to be converted (8 or 10)
When the SAM and CONV values are known, write
them to the AD_TIME register. Do not write to this
register while a conversion is in progress; the results
are unpredictable.
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