Microchip Technology PIC16C63A, Operator'S Manual

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2000 Microchip Technology Inc. DS30605C-page 79
PIC16C63A/65B/73B/74B
12.0 ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The 8-bit Analog-to-Digital (A/D) converter module has
five inputs for the PIC16C73B and eight for the
PIC16C74B.
The A/D allows conversion of an analog input signal to
a corresponding 8-bit digital number. The output of the
sample and hold is the input into the converter, which
generates the result via successive approximation. The
analog reference voltage is software selectable to
either the device’s positive supply voltage (V
DD
), or the
voltage level on the RA3/AN3/V
REF
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/D’s internal RC oscillator.
The A/D module has three registers. These registers
are:
• A/D Result Register (ADRES)
• A/D Control Register 0 (ADCON0)
• A/D Control Register 1 (ADCON1)
The ADCON0 register, shown in Register 12-1, con-
trols the operation of the A/D module. The ADCON1
register, shown in Register 12-2, configures the func-
tions of the port pins. The port pins can be configured
as analog inputs (RA3 can also be a voltage reference),
or as digital I/O.
Additional information on using the A/D module can be
found in the PICmicro™ Mid-Range MCU Family Ref-
erence Manual (DS33023) and in Application Note,
AN546.
REGISTER 12-1: ADCON0 REGISTER (ADDRESS 1Fh)
Note: The PIC16C63A and PIC16C65B do not
include A/D modules. ADCON0, ADCON1
and ADRES registers are not imple-
mented. ADIF and ADIE bits are reserved
and should be maintained clear.
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 U-0 R/W-0
ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE — ADON
bit 7 bit 0
bit 7-6 ADCS1:ADCS0: A/D Conversion Clock Select bits
00
= F
OSC
/2
01
= F
OSC
/8
10
= F
OSC
/32
11
= F
RC
(clock derived from the internal A/D module RC oscillator)
bit 5-3 CHS2:CHS0: Analog Channel Select bits
000
= channel 0, (RA0/AN0)
001
= channel 1, (RA1/AN1)
010
= channel 2, (RA2/AN2)
011
= channel 3, (RA3/AN3)
100
= channel 4, (RA5/AN4)
101
= channel 5, (RE0/AN5)
(1)
110
= channel 6, (RE1/AN6)
(1)
111
= channel 7, (RE2/AN7)
(1)
bit 2 GO/DONE: A/D Conversion Status bit
If ADON = 1:
1
= A/D conversion in progress (setting this bit starts the A/D conversion)
0
= A/D conversion not in progress (this bit is automatically cleared by hardware when the A/D
conversion is complete)
bit 1 Unimplemented: Read as '0'
bit 0 ADON: A/D On bit
1
= A/D converter module is operating
0
= A/D converter module is shut-off and consumes no operating current
Note 1: A/D channels 5, 6 and 7 are implemented on the PIC16C74B only.
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