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PIC18F2450/4450
2006 Microchip Technology Inc.
Advance Information
DS39760A-page 177
The value 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.
After the A/D module has been configured as desired, the
selected channel must be acquired before the conver-
sion is started. The analog input channels must have
their corresponding TRIS bits selected as an input. To
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 register)
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 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 3 TAD is
required before the next acquisition starts.
FIGURE 16-2:
A/D TRANSFER FUNCTION
FIGURE 16-3:
ANALOG INPUT MODEL
Dig
it
a
lCo
d
e
Ou
tp
u
t
3FEh
003h
002h
001h
000h
0.
5
LS
B
1
L
S
B
1.
5
LS
B
2
L
S
B
2.
5
LS
B
102
2
L
S
B
10
22
.5
L
S
B
3
L
S
B
Analog Input Voltage
3FFh
102
3
L
S
B
10
23
.5
L
S
B
VAIN
CPIN
Rs
ANx
5 pF
VT = 0.6V
ILEAKAGE
RIC
≤ 1k
Sampling
Switch
SS
RSS
CHOLD = 25 pF
VSS
VDD
±100 nA
Legend: CPIN
VT
ILEAKAGE
RIC
SS
CHOLD
= Input Capacitance
= Threshold Voltage
= Leakage Current at the pin due to
= Interconnect Resistance
= Sampling Switch
= Sample/hold Capacitance (from DAC)
various junctions
= Sampling Switch Resistance
RSS
VDD
6V
Sampling Switch
5V
4V
3V
2V
12
3
4
(k
Ω)