Datasheet

PIC16C77X
 1999-2013 Microchip Technology Inc. Advance Information DS30275B-page 119
The value that is in the ADRESH and ADRESL regis-
ters are not modified for a Power-on Reset. The
ADRESH and ADRESL registers will contain unknown
data after a Power-on Reset.
After the A/D module has been configured as desired,
the selected channel must be acquired before the con-
version is started. The analog input channels must
have their corresponding TRIS bits selected as an
input. To determine acquisition time, see Section 11.6.
After this acquisition time has elapsed the A/D conver-
sion can be started. The following steps should be fol-
lowed for doing an A/D conversion:
11.2 Configuring the A/D Module
11.3 Configuring Analog Port Pins
The ADCON1 and TRIS registers control the operation
of the A/D port pins. The port pins that are desired as
analog inputs must have their corresponding TRIS bit
set (input). If the TRIS bit is cleared (output), the digital
output level (V
OH or VOL) will be converted.
The A/D operation is independent of the state of the
CHS3:CHS0 bits and the TRIS bits.
11.3.1 CONFIGURING THE REFERENCE
VOLTAGES
The VCFG bits in the ADCON1 register configure the
A/D module reference inputs. The reference high
input can come from an internal reference (VRH) or
(VRL), an external reference (V
REF+), or AVDD. The
low reference input can come from an internal refer-
ence (VRL), an external reference (V
REF-), or AVSS. If
an external reference is chosen for the reference high
or reference low inputs, the port pin that multiplexes
the incoming external references is configured as an
analog input, regardless of the values contained in the
A/D port configuration bits (PCFG3:PCFG0).
After the A/D module has been configured as desired.
and the analog input channels have their correspond-
ing TRIS bits selected for port inputs, the selected
channel must be acquired before conversion is
started. The A/D conversion cycle can be initiated by
setting the GO/DONE
bit. The A/D conversion begins,
and lasts for 13T
AD. The following steps should be fol-
lowed for performing an A/D conversion:
1. Configure the A/D module
• Configure analog pins / voltage reference /
and digital I/O (ADCON1)
• Select A/D input channel (ADCON0)
• Select A/D conversion clock (ADCON0)
• Turn on A/D module (ADCON0)
2. Configure A/D interrupt (if required)
• Clear ADIF bit
• Set ADIE bit
• Set PEIE bit
• Set GIE bit
3. Wait the required acquisition time (3T
AD)
4. Start conversion
• Set GO/DONE
bit (ADCON0)
5. Wait 13T
AD until A/D conversion is complete, by
either:
• Polling for the GO/DONE
bit to be cleared
OR
• Waiting for the A/D interrupt
6. Read A/D Result registers (ADRESH and
ADRESL), clear ADIF if required.
7. For next conversion, go to step 1, step 2 or step
3 as required.
Clearing the GO/DONE
bit during a conversion will
abort the current conversion. The ADRESH and
ADRESL registers WILL be updated with the partially
completed A/D conversion value. That is, the ADRESH
and ADRESL registers WILL contain the value of the
current incomplete conversion.
Note 1: When reading the PORTA or PORTE reg-
ister, all pins configured as analog input
channels will read as cleared (a low level).
When reading the PORTB register, all
pins configured as analog input channels
will read as set (a high level). Pins config-
ured as digital inputs, will convert an ana-
log input. Analog levels on a digitally
configured input will not affect the conver-
sion accuracy.
Note 2: Analog levels on any pin that is defined as
a digital input (including the ANx pins),
may cause the input buffer to consume
current that is out of the devices specifica-
tion.
Note: Do not set the ADON bit and the
GO/DONE
bit in the same instruction.
Doing so will cause the GO/DONE
bit to be
automatically cleared.
774.book Page 119 Tuesday, January 29, 2013 12:02 PM