Microchip Technology MA180025 Data Sheet
2010 Microchip Technology Inc.
DS39933D-page 297
PIC18F87J90 FAMILY
21.7
A/D Converter Calibration
The A/D Converter, in the PIC18F87J90 family of
devices, includes a self-calibration feature which com-
pensates for any offset generated within the module.
The calibration process is automated and is initiated by
setting the ADCAL bit (ADCON0<7>). The next time
the GO/DONE bit is set, the module will perform a
“dummy” conversion (that is, with reading none of the
input channels) and store the resulting value internally
to compensate for the offset. Thus, subsequent offsets
will be compensated.
The calibration process assumes that the device is in a
relatively steady-state operating condition. If A/D
calibration is used, it should be performed after each
device Reset or if there are other major changes in
operating conditions.
devices, includes a self-calibration feature which com-
pensates for any offset generated within the module.
The calibration process is automated and is initiated by
setting the ADCAL bit (ADCON0<7>). The next time
the GO/DONE bit is set, the module will perform a
“dummy” conversion (that is, with reading none of the
input channels) and store the resulting value internally
to compensate for the offset. Thus, subsequent offsets
will be compensated.
The calibration process assumes that the device is in a
relatively steady-state operating condition. If A/D
calibration is used, it should be performed after each
device Reset or if there are other major changes in
operating conditions.
21.8
Operation in Power-Managed
Modes
Modes
The selection of the automatic acquisition time and A/D
conversion clock is determined, in part, by the clock
source and frequency while in a power-managed
mode.
conversion clock is determined, in part, by the clock
source and frequency while in a power-managed
mode.
If the A/D is expected to operate while the device is in
a power-managed mode, the ACQT<2:0> and
ADCS<2:0> bits in ADCON2 should be updated in
accordance with the power-managed mode clock that
will be used. After the power-managed mode is entered
(either of the power-managed Run modes), an A/D
acquisition or conversion may be started. Once an
acquisition or conversion is started, the device should
continue to be clocked by the same power-managed
mode clock source until the conversion has been com-
pleted. If desired, the device may be placed into the
corresponding power-managed Idle mode during the
conversion.
If the power-managed mode clock frequency is less
than 1 MHz, the A/D RC clock source should be
selected.
Operation in Sleep mode requires the A/D RC clock to
be selected. If bits, ACQT<2:0>, are set to ‘000’ and a
conversion is started, the conversion will be delayed
one instruction cycle to allow execution of the SLEEP
instruction and entry to Sleep mode. The IDLEN and
SCSx bits in the OSCCON register must have already
been cleared prior to starting the conversion.
a power-managed mode, the ACQT<2:0> and
ADCS<2:0> bits in ADCON2 should be updated in
accordance with the power-managed mode clock that
will be used. After the power-managed mode is entered
(either of the power-managed Run modes), an A/D
acquisition or conversion may be started. Once an
acquisition or conversion is started, the device should
continue to be clocked by the same power-managed
mode clock source until the conversion has been com-
pleted. If desired, the device may be placed into the
corresponding power-managed Idle mode during the
conversion.
If the power-managed mode clock frequency is less
than 1 MHz, the A/D RC clock source should be
selected.
Operation in Sleep mode requires the A/D RC clock to
be selected. If bits, ACQT<2:0>, are set to ‘000’ and a
conversion is started, the conversion will be delayed
one instruction cycle to allow execution of the SLEEP
instruction and entry to Sleep mode. The IDLEN and
SCSx bits in the OSCCON register must have already
been cleared prior to starting the conversion.
TABLE 21-2:
SUMMARY OF A/D REGISTERS
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset
Values
on page
INTCON
GIE/GIEH PEIE/GIEL TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
PIR1
—
ADIF
RC1IF
TX1IF
SSPIF
—
TMR2IF
TMR1IF
PIE1
—
ADIE
RC1IE
TX1IE
SSPIE
—
TMR2IE
TMR1IE
IPR1
—
ADIP
RC1IP
TX1IP
SSPIP
—
TMR2IP
TMR1IP
PIR3
—
LCDIF
RC2IF
TX2IF
CTMUIF
CCP2IF
CCP1IF
RTCCIF
62
PIE3
—
LCDIE
RC2IE
TX2IE
CTMUIE
CCP2IE
CCP1IE
RTCCIE
IPR3
—
LCDIP
RC2IP
TX2IP
CTMUIP
CCP2IP
CCP1IP
RTCCIP
ADRESH
A/D Result Register High Byte
ADRESL
A/D Result Register Low Byte
ADCON0
ADCAL
—
CHS3
CHS2
CHS1
CHS0
GO/DONE
ADON
ADCON1
TRIGSEL
—
VCFG1
VCFG0
PCFG3
PCFG2
PCFG1
PCFG0
ADCON2
ADFM
—
ACQT2
ACQT1
ACQT0
ADCS2
ADCS1
ADCS0
CCP2CON
—
—
DC2B1
DC2B0
CCP2M3 CCP2M2 CCP2M1
CCP2M0
PORTA
RA7
(1)
RA6
(1)
RA5
RA4
RA3
RA2
RA1
RA0
TRISA
TRISA7
(1)
TRISA6
(1)
TRISA5
TRISA4
TRISA3
TRISA2
TRISA1
TRISA0
PORTF
RF7
RF6
RF5
RF4
RF3
RF2
RF1
—
TRISF
TRISF5
TRISF4
TRISF5
TRISF4
TRISF3
TRISF2
TRISF1
—
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used for A/D conversion.
Note 1: RA<7:6> and their associated latch and direction bits are configured as port pins only when the internal
Note 1: RA<7:6> and their associated latch and direction bits are configured as port pins only when the internal
oscillator is selected as the default clock source (FOSC2 Configuration bit = 0); otherwise, they are
disabled and these bits read as ‘0’.
disabled and these bits read as ‘0’.