PIC18FXX20
The value in the ADRESH/ADRESL registers is not
The following steps should be followed to do an A/D
conversion:
1. Configure the A/D module:
modified
for
a
Power-on
Reset.
The
ADRESH/ADRESL registers will contain unknown data
after a Power-on Reset.
• Configure analog pins, voltage reference and
digital I/O (ADCON1)
• Select A/D input channel (ADCON0)
• Select A/D conversion clock (ADCON2)
• Turn on A/D module (ADCON0)
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.
After this acquisition time has elapsed, the A/D
conversion can be started.
2. Configure A/D interrupt (if desired):
• Clear ADIF bit
• Set ADIE bit
• Set GIE bit
3. Wait the required acquisition time.
4. Start conversion:
• Set GO/DONE bit (ADCON0 register)
5. 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
6. Read A/D Result registers (ADRESH:ADRESL);
clear bit ADIF, if required.
7. For next conversion, go to step 1 or step 2, as
required. The A/D conversion time per bit is
defined as TAD. A minimum wait of 2 TAD is
required before next acquisition starts.
FIGURE 19-2:
ANALOG INPUT MODEL
VDD
Sampling
Switch
VT = 0.6V
ANx
SS
RIC ≤ 1k
RSS
Rs
CPIN
5 pF
I leakage
± 500 nA
VAIN
CHOLD = 120 pF
VT = 0.6V
VSS
Legend: CPIN
VT
= input capacitance
= threshold voltage
6V
5V
I LEAKAGE = leakage current at the pin due to
VDD 4V
3V
various junctions
= interconnect resistance
= sampling switch
RIC
SS
2V
CHOLD
RSS
= sample/hold capacitance (from DAC)
= sampling switch resistance
5
6
7
8 9 10 11
Sampling Switch ( kΩ )
2003 Microchip Technology Inc.
Advance Information
DS39609A-page 217
MICROCHIP [ MICROCHIP ]
