Datasheet

PIC16F882/883/884/886/887
DS41291G-page 106  2006-2012 Microchip Technology Inc.
9.1.6 RESULT FORMATTING
The 10-bit A/D conversion result can be supplied in two
formats, left justified or right justified. The ADFM bit of
the ADCON0 register controls the output format.
Figure 9-3 shows the two output formats.
FIGURE 9-3: 10-BIT A/D CONVERSION RESULT FORMAT
9.2 ADC Operation
9.2.1 STARTING A CONVERSION
To enable the ADC module, the ADON bit of the
ADCON0 register must be set to a ‘1’. Setting the GO/
DONE bit of the ADCON0 register to a ‘1’ will start the
Analog-to-Digital conversion.
9.2.2 COMPLETION OF A CONVERSION
When the conversion is complete, the ADC module will:
• Clear the GO/DONE
bit
• Set the ADIF flag bit
• Update the ADRESH:ADRESL registers with new
conversion result
9.2.3 TERMINATING A CONVERSION
If a conversion must be terminated before completion,
the GO/DONE
bit can be cleared in software. The
ADRESH:ADRESL registers will not be updated with
the partially complete Analog-to-Digital conversion
sample. Instead, the ADRESH:ADRESL register pair
will retain the value of the previous conversion. Addi-
tionally, a 2 T
AD delay is required before another acqui-
sition can be initiated. Following this delay, an input
acquisition is automatically started on the selected
channel.
9.2.4 ADC OPERATION DURING SLEEP
The ADC module can operate during Sleep. This
requires the ADC clock source to be set to the F
RC
option. When the FRC clock source is selected, the
ADC waits one additional instruction before starting the
conversion. This allows the SLEEP instruction to be
executed, which can reduce system noise during the
conversion. If the ADC interrupt is enabled, the device
will wake-up from Sleep when the conversion
completes. If the ADC interrupt is disabled, the ADC
module is turned off after the conversion completes,
although the ADON bit remains set.
When the ADC clock source is something other than
F
RC, a SLEEP instruction causes the present conver-
sion to be aborted and the ADC module is turned off,
although the ADON bit remains set.
9.2.5 SPECIAL EVENT TRIGGER
The ECCP Special Event Trigger allows periodic ADC
measurements without software intervention. When
this trigger occurs, the GO/DONE bit is set by hardware
and the Timer1 counter resets to zero.
Using the Special Event Trigger does not assure
proper ADC timing. It is the user’s responsibility to
ensure that the ADC timing requirements are met.
See Section 11.0 “Capture/Compare/PWM Modules
(CCP1 and CCP2)” for more information.
ADRESH ADRESL
(ADFM = 0)MSB LSB
bit 7 bit 0 bit 7 bit 0
10-bit A/D Result Unimplemented: Read as ‘0’
(ADFM = 1)
MSB LSB
bit 7 bit 0 bit 7 bit 0
Unimplemented: Read as ‘0’ 10-bit A/D Result
Note: The GO/DONE bit should not be set in the
same instruction that turns on the ADC.
Refer to Section 9.2.6 “A/D Conversion
Procedure”.
Note: A device Reset forces all registers to their
Reset state. Thus, the ADC module is
turned off and any pending conversion is
terminated.