PIC16F877-20L Datasheet, PDF (116/218 Pages) Microchip Technology – 28/40-Pin 8-Bit CMOS FLASH Microcontrollers

PIC16F87X
11.4 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 2TAD wait is required before the next
acquisition is started. After this 2TAD wait, acquisition
on the selected channel is automatically started. The
GO/DONE bit can then be set to start the conversion.
In Figure 11-3, after the GO bit is set, the first time seg-
ment 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 11-3:
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
11.4.1 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
FIGURE 11-4:
A/D RESULT JUSTIFICATION
Format Select bit (ADFM) controls this justification.
Figure 11-4 shows the operation of the A/D result justi-
fication. The extra bits are loaded with ’0’s’. When an
A/D result will not overwrite these locations (A/D dis-
able), 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
DS30292D-page 116
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