Programming The A/D Time Register - Intel 8XC196MC User Manual

8XC196MC, MD, MH USER'S MANUAL
AD_RESULT (Write)
The high byte of the A/D result (AD_RESULT) register can be written to set the reference voltage for
the A/D threshold-detection modes.
15
REFV7 REFV6
7
— —
Bit Bit
Number Mnemonic
15:8 REFV7:0
7:0 —
Figure 12-3. A/D Result (AD_RESULT) Register — Write Format

12.4.3 Programming the A/D Time Register

Two parameters, sample time and conversion time, control the time required for an A/D conver-
sion. 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 con-
version 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 cir-
cuitry to settle and resolve the voltage. Excessively long conversion times allow the sample ca-
pacitor to discharge, degrading accuracy.
The AD_TIME register (Figure 12-4) specifies the A/D sample and conversion times. To avoid
erroneous conversion results, use the T
appropriate values.
12-6
REFV5 REFV4
— —
Reference Voltage
These bits specify the threshold value. This selects a reference voltage
that is compared with an analog input pin. When the voltage on the
analog input pin crosses over (detect high) or under (detect low) the
threshold value, the A/D conversion complete interrupt pending bit is set.
Use the following formula to determine the value to write to this register
for a given threshold voltage.
desired threshold voltage
---------------------------------------------------------------------------------- -
reference voltage
=
Reserved; for compatibility with future devices, write zeros to these bits.
and T
SAM CONV
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Reset State (MC, MD):
Reset State (MH):
REFV3 REFV2
— —
Function
×
256
V ANG ND
–
REF
specifications on the datasheet to determine
Address: 1FAAH
FFC0H
7FC0H
8
REFV1 REFV0
0
— —