Datasheet

© 2009 Microchip Technology Inc. DS39689F-page 233
PIC18F2221/2321/4221/4321 FAMILY
20.0 10-BIT ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The Analog-to-Digital (A/D) converter module has
10 inputs for the 28-pin devices and 13 for the 40/44-pin
devices. This module allows conversion of an analog
input signal to a corresponding 10-bit digital number.
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, programmed acquisition time and justification.
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 CHS<3:0>: 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)
(1,2)
0110 = Channel 6 (AN6)
(1,2)
0111 = Channel 7 (AN7)
(1,2)
1000 = Channel 8 (AN8)
1001 = Channel 9 (AN9)
1010 = Channel 10 (AN10)
1011 = Channel 11 (AN11)
1100 = Channel 12 (AN12
1101 = Unimplemented
(2)
1110 = Unimplemented
(2)
1111 = Unimplemented
(2)
Note 1: These channels are not implemented on 28-pin devices.
2: Performing a conversion on unimplemented channels will return a floating input
measurement.
bit 1 GO/DONE
: A/D Conversion Status bit
When ADON = 1:
1 = A/D conversion in progress
0 = A/D Idle
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