Datasheet

 2003-2013 Microchip Technology Inc. DS39612C-page 233
PIC18F6525/6621/8525/8621
20.0 10-BIT ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The analog-to-digital (A/D) converter module has
12 inputs for the PIC18F6525/6621 devices and 16 for
the PIC18F8525/8621 devices. This module allows
conversion of an analog input signal to a corresponding
10-bit digital number.
A new feature for the A/D converter is the addition of
programmable acquisition time. This feature allows the
user to select a new channel for conversion and setting
the GO/DONE
bit immediately. When the GO/DONE bit
is set, the selected channel is sampled for the
programmed acquisition time before a conversion is
actually started. This removes the firmware overhead
that may have been required to allow for an acquisition
(sampling) period (see Register 20-3 and Section 20.5
“A/D Conversions”).
The module has five registers:
• A/D Result High Register (ADRESH)
• A/D Result Low Register (ADRESL)
• A/D Control Register 0 (ADCON0)
• A/D Control Register 1 (ADCON1)
• A/D Control Register 2 (ADCON2)
The ADCON0 register, shown in Register 20-1,
controls the operation of the A/D module. The
ADCON1 register, shown in Register 20-2, configures
the functions of the port pins. The ADCON2 register,
shown in Register 20-3, configures the A/D clock
source, justification and auto-acquisition time.
REGISTER 20-1: ADCON0: A/D CONTROL REGISTER 0
U-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
— — CHS3 CHS2 CHS1 CHS0 GO/DONE ADON
bit 7 bit 0
bit 7-6 Unimplemented: Read as ‘0’
bit 5-2 CHS3:CHS0: Analog Channel Select bits
0000 = Channel 0 (AN0)
0001 = Channel 1 (AN1)
0010 = Channel 2 (AN2)
0011 = Channel 3 (AN3)
0100 = Channel 4 (AN4)
0101 = Channel 5 (AN5)
0110 = Channel 6 (AN6)
0111 = Channel 7 (AN7)
1000 = Channel 8 (AN8)
1001 = Channel 9 (AN9)
1010 = Channel 10 (AN10)
1011 = Channel 11 (AN11)
1100 = Channel 12 (AN12)
(1)
1101 = Channel 13 (AN13)
(1)
1110 = Channel 14 (AN14)
(1)
1111 = Channel 15 (AN15)
(1)
Note 1: These channels are not available on the PIC18F6525/6621 (64-pin) devices.
bit 1 GO/DONE
: A/D Conversion Status bit
When ADON =
1:
1 = A/D conversion in progress (setting this bit starts the A/D conversion which is automatically
cleared by hardware when the A/D conversion is complete)
0 = A/D conversion not in progress
bit 0 ADON: A/D On bit
1 = A/D converter module is enabled
0 = A/D converter module is disabled
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown