Intel 8XC196NT, User Manual

Page: 278 / 597

11-7
ANALOG-TO-DIGITAL CONVERTER
The AD_TIME register (Figure 11-4) specifies the A/D sample and conversion times. To avoid
erroneous conversion results, use the T
SAM
and T
CONV
specifications on the datasheet to determine
appropriate values.
AD_TIME
Address:
Reset State:
1FAFH
FFH
The A/D time (AD_TIME) register programs the sample window time and the conversion time for each
bit.
7 0
SAM2 SAM1 SAM0 CONV4 CONV3 CONV2 CONV1 CONV0
Bit
Number
Bit
Mnemonic
Function
7:5 SAM2:0 A/D Sample Time
These bits specify the sample time. Use the following formula to
compute the sample time.
where:
SAM = 1 to 7
T
SAM
= the sample time, in
µ
sec, from the data sheet
F
OSC
= the XTAL1 frequency, in MHz
4:0 CONV4:0 A/D Convert Time
These bits specify the conversion time for each bit. Use the following
formula to compute the conversion time.
where:
CONV = 2 to 31
T
CONV
= the conversion time, in
µ
sec, from the data sheet
F
OSC
= the XTAL1 frequency, in MHz
B = the number of bits to be converted (8 or 10)
NOTES:
1.
This register programs the speed at which the A/D can run — not the speed at which it can con-
vert correctly. Consult the data sheet for recommended values.
2. Initialize the AD_TIME register before initializing the AD_COMMAND register.
3. Do not write to this register while a conversion is in progress; the results are unpredictable.
Figure 11-4. A/D Time (AD_TIME) Register
SAM
T
SA M
F
O SC
×
2
–
8
--------------------------------------------
=
CO NV
T
CO NV
F
OS C
×
3
–
2 B
×
-----------------------------------------------
1
–
=