PIC18F2431-I/SP Microchip Technology Inc., PIC18F2431-I/SP Datasheet - Page 141

• Manufacturer Part Number: PIC18F2431-I/SP
• Description: Microcontroller; 16 KB Flash; 768 RAM; 256 EEPROM; 24 I/O; 28-Pin-SPDIP
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F2431-I/SP

• A/d Inputs: 5-Channel, 10-Bit
• Cpu Speed: 10 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 24
• Interface: I2C/SPI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 28-pin SPDIP
• Programmable Memory: 16K Bytes
• Ram Size: 768 Bytes
• Speed: 40 MHz
• Timers: 1-8-bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

12.2
A crystal oscillator circuit is built-in between pins T1OSI
(input) and T1OSO (amplifier output). It is enabled by
setting control bit T1OSCEN (T1CON<3>). The oscilla-
tor is a low-power oscillator rated for 32 kHz crystals. It
will continue to run during all power-managed modes.
The circuit for a typical LP oscillator is shown in
Figure 12-3. Table 12-1 shows the capacitor selection
for the Timer1 oscillator.
The user must provide a software time delay to ensure
proper start-up of the Timer1 oscillator.
FIGURE 12-3:
TABLE 12-1:
 2003 Microchip Technology Inc.
Osc Type
Note 1: Microchip suggests this value as a starting
Note:
LP
2: Higher capacitance increases the stability
3: Since each resonator/crystal has its own
4: Capacitor values are for design guidance
Timer1 Oscillator
33 pF
33 pF
C1
C2
See the notes with Table 12-1 for additional
information about capacitor selection.
point in validating the oscillator circuit.
of the oscillator, but also increases the
start-up time.
characteristics, the user should consult
the resonator/crystal manufacturer for
appropriate
components.
only.
32 kHz
Freq
CAPACITOR SELECTION FOR
THE TIMER OSCILLATOR
32.768 kHz
XTAL
EXTERNAL
COMPONENTS FOR THE
TIMER1 LP OSCILLATOR
values
27 pF
T1OSI
T1OSO
C1
PIC18FXXXX
(1)
of
27 pF
PIC18F2331/2431/4331/4431
external
C2
(1)
Preliminary
12.3
The Timer1 oscillator for PIC18F2331/2431/4331/4431
devices incorporates an additional low-power feature.
When this option is selected, it allows the oscillator to
automatically reduce its power consumption when the
microcontroller is in Sleep mode. During normal device
operation, the oscillator draws full current. As high
noise environments may cause excessive oscillator
instability in Sleep mode, this option is best suited for
low noise applications where power conservation is an
important design consideration.
The low-power option is enabled by clearing the
T1OSCMX bit (CONFIG3L<5>). By default, the option
is disabled, which results in a more-or-less constant
current draw for the Timer1 oscillator.
Due to the low power nature of the oscillator, it may also
be sensitive to rapidly changing signals in close
proximity.
The oscillator circuit, shown in Figure 12-3, should be
located as close as possible to the microcontroller.
There should be no circuits passing within the oscillator
circuit boundaries other than V
If a high-speed circuit must be located near the oscilla-
tor (such as the CCP1 pin in output compare or PWM
mode, or the primary oscillator using the OSC2 pin), a
grounded guard ring around the oscillator circuit, as
shown in Figure 12-4, may be helpful when used on a
single sided PCB, or in addition to a ground plane.
FIGURE 12-4:
Note: Not drawn to scale.
Timer1 Oscillator Layout
Considerations
OSCILLATOR CIRCUIT
WITH GROUNDED GUARD
RING
SS
OSC1
RC0
V
V
OSC2
RC1
RC2
or V
DD
SS
DS39616B-page 139
DD
.