PIC18F2420-I/SOC01 Microchip, PIC18F2420-I/SOC01 Datasheet - Page 229

• Manufacturer Part Number: PIC18F2420-I/SOC01
• Description: 28 pin, 16 kb flash, 3804 ram, 25 i/o...
• Manufacturer: Microchip

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
conversion 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.
2.
3.
4.
FIGURE 19-3:
© 2008 Microchip Technology Inc.
Configure the A/D module:
• Configure analog pins, voltage reference and
• Select A/D input channel (ADCON0)
• Select A/D acquisition time (ADCON2)
• Select A/D conversion clock (ADCON2)
• Turn on A/D module (ADCON0)
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)
digital I/O (ADCON1)
Legend: C
V
AIN
Rs
V
I
R
SS
C
R
LEAKAGE
ANALOG INPUT MODEL
PIN
T
IC
HOLD
SS
ANx
C
5 pF
PIN
= Input Capacitance
= Threshold Voltage
= Leakage Current at the pin due to
= Interconnect Resistance
= Sampling Switch
= Sample/Hold Capacitance (from DAC)
= Sampling Switch Resistance
various junctions
V
PIC18F2420/2520/4420/4520
DD
V
V
T
T
= 0.6V
= 0.6V
I
±100 nA
5.
6.
7.
FIGURE 19-2:
LEAKAGE
R
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
required before the next acquisition starts.
IC
3FFh
3FEh
003h
002h
001h
000h
≤ 1k
V
DD
SS
Sampling
Switch
AD
6V
5V
4V
3V
2V
R
. A minimum wait of 2 T
SS
A/D TRANSFER FUNCTION
Analog Input Voltage
Sampling Switch
1
V
SS
2
C
HOLD
3
DS39631E-page 227
= 25 pF
4
(kΩ)
AD
is