Programming The A/D Result Register (For Threshold Detection Only); Programming The A/D Time Register - Intel 8XC196K Series User Manual

8XC196K x , J x , CA USER'S MANUAL

11.4.2 Programming the A/D Result Register (for Threshold Detection Only)

To use the threshold-detection modes, you must first write a value to the high byte of
AD_RESULT to set the desired reference (threshold) voltage.
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 11-3. A/D Result (AD_RESULT) Register — Write Format

11.4.3 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.
11-6
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 interrupt flag is set.
Use the following formula to determine the value to write this register for
a given threshold voltage.
desired threshold voltage
---------------------------------------------------------------------------------- -
reference voltage
=
Reserved; for compatibility with future devices, write zeros to these bits.
Reset State:
REFV3 REFV2
— —
Function
×
256
V ANG ND
–
REF
Address: 1FAAH
7F80H
8
REFV1 REFV0
0
— —