
2004 Microchip Technology Inc.
Preliminary
DS39637A-page 251
PIC18F2480/2580/4480/4580
The value in the ADRESH/ADRESL registers is not
modified for a Power-on Reset. The ADRESH/ADRESL
registers will contain unknown data after a Power-on
Reset.
After the A/D module has been configured as desired,
the selected channel must be acquired before the con-
version is started. The analog input channels must
have their corresponding TRIS bits selected as an
input. To determine acquisition time, see
Section 19.1
“A/D Acquisition Requirements”
. After this acquisi-
tion time has elapsed, the A/D conversion can be
started. An acquisition time can be programmed to
occur between setting the GO/DONE bit and the actual
start of the conversion.
The following steps should be followed to perform an
A/D conversion:
1.
Configure the A/D module:
Configure analog pins, voltage reference and
digital I/O (ADCON1)
Select A/D input channel (ADCON0)
Select A/D acquisition time (ADCON2)
Select A/D conversion clock (ADCON2)
Turn on A/D module (ADCON0)
2.
Configure A/D interrupt (if desired):
Clear ADIF bit
Set ADIE bit
Set GIE bit
Wait the required acquisition time (if required).
Start conversion:
Set GO/DONE bit (ADCON0 register)
Wait for A/D conversion to complete, by either:
Polling for the GO/DONE bit to be cleared
OR
Waiting for the A/D interrupt
Read A/D Result registers (ADRESH:ADRESL);
clear bit ADIF, if required.
For next conversion, go to step 1 or step 2, as
required. The A/D conversion time per bit is
defined as T
AD
. A minimum wait of 2 T
AD
is
required before next acquisition starts.
3.
4.
5.
6.
7.
FIGURE 19-2:
ANALOG INPUT MODEL
V
AIN
C
PIN
5 pF
Rs
ANx
V
DD
V
T
= 0.6V
V
T
= 0.6V
I
LEAKAGE
± 500 nA
R
IC
≤
1k
Sampling
Switch
SS
R
SS
C
HOLD
= 120 pF
V
SS
6V
5V
4V
3V
2V
Sampling Switch
5 6 7 8 9 10 11
(k
)
V
DD
Legend:
C
PIN
V
T
I
LEAKAGE
R
IC
SS
C
HOLD
R
SS
= input capacitance
= threshold voltage
= leakage current at the pin due to
various junctions
= interconnect resistance
= sampling switch
= sample/hold capacitance (from DAC)
= sampling switch resistance