PIC18F24 MICROCHIP [Microchip Technology], PIC18F24 Datasheet - Page 246

• Manufacturer Part Number: PIC18F24
• Description: 28/40-Pin High-Performance, Enhanced Flash Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

The value that is 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 20.1
“A/D Acquisition Requirements”. After this acquisi-
tion time has elapsed, the A/D conversion can be
started. The following steps should be followed for
doing an A/D conversion:
1.
2.
3.
4.
5.
FIGURE 20-2:
DS41159D-page 244
PIC18FXX8
Configure the A/D module:
• Configure analog pins, voltage reference and
• Select A/D input channel (ADCON0)
• Select A/D conversion clock (ADCON0)
• 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.
Start conversion:
• Set GO/DONE bit (ADCON0)
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
digital I/O (ADCON1)
Legend: C
V
AIN
Rs
V
I
R
SS
C
LEAKAGE
T
PIN
IC
HOLD
ANx
ANALOG INPUT MODEL
C
5 pF
PIN
= input capacitance
= threshold voltage
= leakage current at the pin due to
= interconnect resistance
= sampling switch
= sample/hold capacitance (from DAC)
various junctions
V
DD
V
V
T
T
= 0.6V
= 0.6V
I
± 500 nA
LEAKAGE
6.
7.
20.1
For the A/D converter to meet its specified accuracy,
the charge holding capacitor (C
to fully charge to the input channel voltage level. The
analog input model is shown in Figure 20-2. The
source impedance (R
switch (R
required to charge the capacitor C
switch (R
(V
at the analog input (due to pin leakage current). The
maximum recommended impedance for analog
sources is 2.5 k . After the analog input channel is
selected (changed), this acquisition must be done
before the conversion can be started.
R
IC
DD
Note:
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 next acquisition starts.
1k
). The source impedance affects the offset voltage
A/D Acquisition Requirements
SS
V
SS
DD
SS
) impedance varies over the device voltage
When the conversion is started, the
holding capacitor is disconnected from the
input pin.
Sampling
Switch
) impedance directly affect the time
6V
5V
4V
3V
2V
R
SS
AD
. A minimum wait of 2 T
S
Sampling Switch
5 6 7 8 9 10 11
 2004 Microchip Technology Inc.
) and the internal sampling
V
SS
C
HOLD
HOLD
= 120 pF
HOLD
) must be allowed
(k )
. The sampling
AD
is