MCP2515-ESLASHML datasheet(55/92 Pages) MICROCHIP

55 / 92 page

 2003-2012 Microchip Technology Inc.

DS21801G-page 55

MCP2515

8.0

OSCILLATOR

The MCP2515 is designed to be operated with a crystal

or ceramic resonator connected to the OSC1 and

OSC2 pins. The MCP2515 oscillator design requires

the use of a parallel cut crystal. Use of a series cut

crystal may give a frequency out of the crystal

manufacturer’s specifications. A typical oscillator circuit

is shown in Figure 8-1. The MCP2515 may also be

driven by an external clock source connected to the

OSC1 pin, as shown in Figure 8-2 and Figure 8-3.

8.1

Oscillator Start-up Timer

The MCP2515 utilizes an Oscillator Start-up Timer

(OST) that holds the MCP2515 in Reset to ensure that

the oscillator has stabilized before the internal state

machine begins to operate. The OST maintains Reset

for the first 128 OSC1 clock cycles after power-up or a

wake-up from Sleep mode occurs. It should be noted

that no SPI protocol operations should be attempted

until after the OST has expired.

8.2

CLKOUT Pin

The CLKOUT pin is provided to the system designer for

use as the main system clock or as a clock input for

other devices in the system. The CLKOUT has an inter-

nal prescaler which can divide FOSC by 1, 2, 4 and 8.

The CLKOUT function is enabled and the prescaler is

selected

via

the

CANCNTRL

(see

The CLKOUT pin will be active upon system Reset and

default to the slowest speed (divide by 8) so that it can

be used as the MCU clock.

When Sleep mode is requested, the MCP2515 will

drive sixteen additional clock cycles on the CLKOUT

pin before entering Sleep mode. The Idle state of the

CLKOUT pin in Sleep mode is low. When the CLKOUT

function is disabled (CANCNTRL.CLKEN = 0) the

CLKOUT pin is in a high-impedance state.

The CLKOUT function is designed to ensure that

thCLKOUT and tlCLKOUT timings are preserved when the

CLKOUT pin function is enabled, disabled or the

prescaler value is changed.

FIGURE 8-1:

CRYSTAL/CERAMIC RESONATOR OPERATION

FIGURE 8-2:

EXTERNAL CLOCK SOURCE

Note:

The maximum frequency on CLKOUT is

specified as 25 MHz (See Table 13-5).

XTAL

OSC2

RS(1)

OSC1

RF(2)

Sleep

To internal logic

Note 1: A series resistor (RS) may be required for AT strip-cut crystals.

2: The feedback resistor (RF ), is typically in the range of 2 to 10 M

.

Clock from

external system

OSC1

OSC2

Open

(1)

Note 1: A resistor to ground may be used to reduce system noise. This may increase system current.

2: Duty cycle restrictions must be observed (see Table 12-1).

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