PIC16F87-E Datasheet, PDF (118/228 Pages) Microchip Technology – 18/20/28-Pin Enhan lashMicrocontrollers with nanoWatt Technology

PIC16F87/88
The ADRESH:ADRESL registers contain the result of
the A/D conversion. When the A/D conversion is
complete, the result is loaded into the A/D Result register
pair, the GO/DONE bit (ADCON0<2>) is cleared and
A/D Interrupt Flag bit, ADIF, is set. The block diagram of
the A/D module is shown in Figure 12-1.
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 inputs.
To determine sample time, see Section 12.1 “A/D
Acquisition Requirements”. After this sample time
has elapsed, the A/D conversion can be started.
These steps should be followed for doing an A/D
conversion:
1. Configure the A/D module:
• Configure analog/digital I/O (ANSEL)
• Configure voltage reference (ADCON1)
• Select A/D input channel (ADCON0)
• Select A/D conversion clock (ADCON0)
• Turn on A/D module (ADCON0)
2. Configure A/D interrupt (if desired):
• Clear ADIF bit
• Set ADIE bit
• SET PEIE bit
• Set GIE bit
3. Wait the required acquisition time.
4. Start conversion:
• Set GO/DONE bit (ADCON0)
5. Wait for A/D conversion to complete, by either:
• Polling for the GO/DONE bit to be cleared
(with interrupts disabled); OR
• Waiting for the A/D interrupt
6. Read A/D Result register pair
(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 the next acquisition starts.
FIGURE 12-1:
A/D BLOCK DIAGRAM
CHS2:CHS0
110
101
100
011
010
VIN
(Input Voltage)
001
A/D
Converter
VREF+
AVDD
000
(Reference
Voltage)
VCFG1:VCFG0
RB7/AN6/PGD/T1OSI
RB6/AN5/PGC/T1OSO/T1CKI
RA4/AN4/T0CKI/C2OUT
RA3/AN3/VREF+/C1OUT
RA2/AN2/CVREF/VREF-
RA1/AN1
RA0/AN0
VREF-
(Reference
Voltage)
AVSS
VCFG1:VCFG0
DS30487C-page 116
 2005 Microchip Technology Inc.