PIC16F818/819
11.5 A/D Operation During Sleep
11.6 Effects of a Reset
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
module will then be turned off, although the ADON bit
will remain set.
A device Reset forces all registers to their Reset state.
The A/D module is disabled and any conversion in
progress is aborted. All A/D input pins are configured
as analog inputs.
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.
11.7 Use of the CCP Trigger
An A/D conversion can be started by the “special event
trigger” of the CCP module. This requires that the
CCP1M3:CCP1M0
bits
(CCP1CON<3:0>)
be
When the A/D clock source is another clock option (not
RC), a SLEEPinstruction 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.
programmed as ‘1011’ and that the A/D module is
enabled (ADON bit is set). When the trigger occurs, the
GO/DONE bit will be set, starting the A/D conversion
and the Timer1 counter will be reset to zero. Timer1 is
reset to automatically repeat the A/D acquisition period
with minimal software overhead (moving the
ADRESH:ADRESL to the desired location). The appro-
priate analog input channel must be selected and the
minimum acquisition done before the “special event
trigger” sets the GO/DONE bit (starts a conversion).
Turning off the A/D places the A/D module in its lowest
current consumption state.
Note:
For the A/D module to operate in Sleep,
the A/D clock source must be set to RC
(ADCS1:ADCS0 = 11). To perform an A/D
conversion in Sleep, ensure the SLEEP
instruction immediately follows the
instruction that sets the GO/DONE bit.
If the A/D module is not enabled (ADON is cleared),
then the “special event trigger” will be ignored by the
A/D module but will still reset the Timer1 counter.
TABLE 11-2: REGISTERS/BITS ASSOCIATED WITH A/D
Value on
all other
Resets
Value on
POR, BOR
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0Bh,8Bh
INTCON
GIE
PEIE TMR0IE INTE RBIE
TMR0IF
INTF
RBIF
0000 000x 0000 000u
10Bh,18Bh
0Ch
8Ch
1Eh
PIR1
PIE1
—
—
ADIF
ADIE
—
—
—
—
SSPIF CCP1IF TMR2IF TMR1IF -0-- 0000 -0-- 0000
SSPIE CCP1IE TMR2IE TMR1IE -0-- 0000 -0-- 0000
xxxx xxxx uuuu uuuu
ADRESH A/D Result Register High Byte
ADRESL A/D Result Register Low Byte
9Eh
xxxx xxxx uuuu uuuu
1Fh
ADCON0 ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE
—
ADON 0000 00-0 0000 00-0
9Fh
ADCON1 ADFM ADCS2
—
—
PCFG3 PCFG2
RA3 RA2
PCFG1 PCFG0 00-- 0000 00-- 0000
05h
PORTA
TRISA
RA7
RA6
RA5
RA4
RA1
RA0
xxx0 0000 uuu0 0000
1111 1111 1111 1111
85h
TRISA7 TRISA6 TRISA5 PORTA Data Direction Register
Legend:
x= unknown, u= unchanged, -= unimplemented, read as ‘0’. Shaded cells are not used for A/D conversion.
2003 Microchip Technology Inc.
DS39598D-page 87
MICROCHIP [ MICROCHIP ]
