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PIC18F258 Datasheet, PDF (241/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN | |||
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PIC18FXX8
The analog reference voltage is software selectable to
either the deviceâs positive and negative supply voltage
(VDD and VSS), or the voltage level on the
RA3/AN3/VREF+ pin and RA2/AN2/VREF- pin.
The A/D converter has a unique feature of being able
to operate while the device is in SLEEP mode. To oper-
ate in SLEEP, the A/D conversion clock must be
derived from the A/Dâs internal RC oscillator.
The output of the sample and hold is the input into the
converter, which generates the result via successive
approximation.
FIGURE 20-1:
A/D BLOCK DIAGRAM
A device RESET forces all registers to their RESET
state. This forces the A/D module to be turned off and
any conversion is aborted.
Each port pin associated with the A/D converter can be
configured as an analog input (RA3 can also be a
voltage reference), or as a digital I/O.
The ADRESH and ADRESL registers contain the result
of the A/D conversion. When the A/D conversion is com-
plete, the result is loaded into the ADRESH/ADRESL
registers, the GO/DONE bit (ADCON0<2>) is cleared,
and A/D interrupt flag bit, ADIF, is set. The block
diagram of the A/D module is shown in Figure 20-1.
CHS2:CHS0
10-bit
Converter
A/D
Reference
voltage
VAIN
(Input Voltage)
VREF+
PCFG0
VDD
VREF-
111
AN7(1)
110
AN6(1)
101
AN5(1)
100
AN4
011
AN3
010
AN2
001
AN1
000
AN0
VSS
Note 1: Channels AN5 through AN7 are not available on PIC18F2X8 devices.
2: All I/O pins have diode protection to VDD and VSS.
 2002 Microchip Technology Inc.
Preliminary
DS41159B-page 239
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