PIC16F870_13 Datasheet, PDF (84/172 Pages) Microchip Technology – 28/40-Pin, 8-Bit CMOS FLASH Microcontrollers

PIC16F870/871
10.4 A/D Conversions
Clearing the GO/DONE bit during a conversion will
abort the current conversion. The A/D result register
pair will NOT be updated with the partially completed
A/D conversion sample. That is, the ADRESH:ADRESL
registers will continue to contain the value of the last
completed conversion (or the last value written to the
ADRESH:ADRESL registers). After the A/D conversion
is aborted, a 2 TAD wait is required before the next
acquisition is started. After this 2 TAD wait, acquisition
on the selected channel is automatically started. The
GO/DONE bit can then be set to start the conversion.
In Figure 10-3, after the GO bit is set, the first time
segment has a minimum of TCY and a maximum of TAD.
Note: The GO/DONE bit should NOT be set in
the same instruction that turns on the A/D.
FIGURE 10-3:
A/D CONVERSION TAD CYCLES
TCY to TAD TAD1 TAD2 TAD3 TAD4 TAD5 TAD6 TAD7 TAD8 TAD9 TAD10 TAD11
b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
Conversion starts
Holding capacitor is disconnected from analog input (typically 100 ns)
Set GO bit
ADRES is loaded
GO bit is cleared
ADIF bit is set
Holding capacitor is connected to analog input
10.4.1 A/D RESULT REGISTERS
The ADRESH:ADRESL register pair is the location
where the 10-bit A/D result is loaded at the completion of
the A/D conversion. This register pair is 16-bits wide.
The A/D module gives the flexibility to left or right justify
the 10-bit result in the 16-bit result register. The A/D For-
FIGURE 10-4:
A/D RESULT JUSTIFICATION
mat Select bit (ADFM) controls this justification.
Figure 10-4 shows the operation of the A/D result justifi-
cation. The extra bits are loaded with ‘0’. When an A/D
result will not overwrite these locations (A/D disable),
these registers may be used as two general purpose
8-bit registers.
ADFM = 1
10-bit Result
ADFM = 0
7
2107
0
0000 00
ADRESH
ADRESL
10-bit Result
Right Justified
7
0765
0
0000 00
ADRESH
ADRESL
10-bit Result
Left Justified
DS30569C-page 84
 2000-2013 Microchip Technology Inc.