PIC18F6393_09 Datasheet, PDF (35/58 Pages) Microchip Technology – 64/80-Pin High Performance, Flash Microcontrollers with LCD Driver, 12-Bit ADC and nanoWatt Technology

PIC18F6393/6493/8393/8493
The value in the ADRESH:ADRESL registers is
unknown following Power-on and Brown-out Resets and
is not affected by any other Reset.
After the A/D module has been configured as desired,
the selected channel must be acquired before the
conversion is started. The analog input channels must
have their corresponding TRIS bits selected as an
input. To determine acquisition time, see Section 2.1
“A/D Acquisition Requirements”. After this acquisi-
tion time has elapsed, the A/D conversion can be
started. An acquisition time can be programmed to
occur between setting the GO/DONE bit and the actual
start of the conversion.
The following steps should be followed to perform 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 acquisition time (ADCON2)
• Select A/D conversion clock (ADCON2)
• Turn on A/D module (ADCON0)
2. Configure A/D interrupt (if desired):
• Clear ADIF bit
• Set ADIE bit
• Set GIE bit
3. Wait the required acquisition time (if required).
4. Start conversion:
• Set GO/DONE bit (ADCON0<1>)
5. Wait for A/D conversion to 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:ADRESL);
clear bit, ADIF, if required.
7. For the next conversion, go to step 1 or step 2,
as required. The A/D conversion time per bit is
defined as TAD. A minimum wait of 2 TAD is
required before the next acquisition starts.
FIGURE 2-2:
A/D TRANSFER FUNCTION
FFFh
FFEh
003h
002h
001h
000h
Analog Input Voltage
FIGURE 2-3:
ANALOG INPUT MODEL
VDD
Rs ^ANx
VT = 0.6V
RIC ≤ 1k
Sampling
Switch
SS _RSS
VAIN
CPIN
5 pF
VT = 0.6V
ILEAKAGE
±100 nA
CHOLD = 25 pF
VSS
Legend: CPIN
= Input Capacitance
VT
= Threshold Voltage
ILEAKAGE = Leakage Current at the pin due to
various junctions
RIC
= Interconnect Resistance
SS
= Sampling Switch
CHOLD = Sample/Hold Capacitance (from DAC)
RSS
= Sampling Switch Resistance
6V
5V
VDD 4V
3V
2V
1 23 4
Sampling Switch (kΩ)
© 2009 Microchip Technology Inc.
DS39896B-page 35