Datasheet

PIC17C7XX
DS30289C-page 188  1998-2013 Microchip Technology Inc.
16.4.1 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
Format Select bit (ADFM) controls this justification.
Figure 16-6 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 disable),
these registers may be used as two general purpose 8-
bit registers.
16.5 A/D Operation During SLEEP
The A/D module can operate during SLEEP mode. This
requires that the A/D clock source be set to RC
(ADCS1:ADCS0 = 11). When the RC clock source is
selected, the A/D module waits one instruction cycle
before starting the conversion. This allows the SLEEP
instruction to be executed, which eliminates all digital
switching noise from the conversion. When the conver-
sion is completed, the GO/DONE
bit will be cleared,
and the result loaded into the ADRES register. If the A/
D interrupt is enabled, the device will wake-up from
SLEEP. If the A/D interrupt is not enabled, the A/D mod-
ule will then be turned off, although the ADON bit will
remain set.
When the A/D clock source is another clock option (not
RC), a SLEEP instruction will cause the present conver-
sion to be aborted and the A/D module to be turned off,
though the ADON bit will remain set.
Turning off the A/D places the A/D module in its lowest
current consumption state.
16.6 Effects of a RESET
A device RESET forces all registers to their RESET
state. This forces the A/D module to be turned off, and
any conversion is aborted.
The value that is in the ADRESH:ADRESL registers is
not modified for a Power-on Reset. The
ADRESH:ADRESL registers will contain unknown data
after a Power-on Reset.
FIGURE 16-6: A/D RESULT JUSTIFICATION
Note: For the A/D module to operate in SLEEP,
the A/D clock source must be set to RC
(ADCS1:ADCS0 = 11). To allow the con-
version to occur during SLEEP, ensure the
SLEEP instruction immediately follows the
instruction that sets the GO/DONE
bit.
10-Bit Result
ADRESH ADRESL
0000 00
ADFM = 0
0
2 1 0 77
10-bits
RESULT
ADRESH ADRESL
10-bits
0000 00
7
0 7 6 5 0
RESULT
ADFM = 1
Right Justified
Left Justified