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PIC16F87XATI/SP Datasheet - Page 129

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The ADRESH:ADRESL registers contain the 10-bit
result of the A/D conversion. When the A/D conversion
is complete, the result is loaded into this A/D Result
register pair, the GO/DONE bit (ADCON0<2>) is cleared
and the A/D interrupt flag bit ADIF is set. The block
diagram of the A/D module is shown in Figure 11-1.
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 inputs.
To determine sample time, see Section 11.1 “A/D
Acquisition Requirements”. After this acquisition
time has elapsed, the A/D conversion can be started.
To do an A/D Conversion, follow these steps:
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 conversion clock (ADCON0)
• Turn on A/D module (ADCON0)
FIGURE 11-1:
A/D BLOCK DIAGRAM
A/D
Converter
V
REF
(Reference
Voltage)
V
REF
(Reference
Voltage)
Note 1: Not available on 28-pin devices.
 2001-2013 Microchip Technology Inc.
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
(interrupts disabled); OR
• Waiting for the A/D interrupt
6.
Read
(ADRESH:ADRESL), clear bit ADIF if required.
7.
For the next conversion, go to step 1 or step 2
as required. The A/D conversion time per bit is
defined as T
CHS2:CHS0
V
AIN
(Input Voltage)
V
DD
+
PCFG3:PCFG0
-
V
SS
PCFG3:PCFG0
PIC16F87XA
A/D
Result
register
pair
.
AD
111
(1)
RE2/AN7
110
(1)
RE1/AN6
101
(1)
RE0/AN5
100
RA5/AN4
011
RA3/AN3/V
+
REF
010
RA2/AN2/V
-
REF
001
RA1/AN1
000
RA0/AN0
DS39582C-page 129

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