MCP25020ISLASHP datasheet(47/66 Pages) MICROCHIP

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DS21664D-page 47

MCP2502X/5X

8.0

SPECIAL FEATURES OF THE

MCP2502X/5X

8.1

Description

There are a number of special circuits in the

MCP2502X/5X that deal with the needs of real-time

applications. These features are intended to maximize

system reliability, minimize cost through elimination of

external

components

and

provide

power-saving

operating modes. These are:

• Oscillator selection

• Reset

- Power-on Reset (POR)

- Power-up Timer (PWRT)

- Oscillator Start-up Timer (OST)

• SLEEP

• In-Circuit Serial Programming

Several oscillator options are offered to allow the

device to fit the application. XT and HS modes allow

the device to support a wide range of crystal

frequencies while the LP crystal option saves power.

Two timers are implemented to offer necessary delays

on power-up. One is the Oscillator Start-up Timer

(OST), intended to keep the device in reset until the

crystal oscillator is stable. The other is the Power-up

Timer (PWRT), which provides a fixed delay of 72 ms

(nominal) on power-up only, designed to keep the part

in reset while the power supply stabilizes. With these

two timers on-chip, most applications need no external

reset circuitry.

SLEEP mode is designed to offer a very low current

power-down mode. The user can wake-up from SLEEP

through external reset, transmit-on-change or CAN bus

activity.

A set of configuration bits are used to select various

options.

FIGURE 8-1:

CRYSTAL/CERAMIC

RESONATOR

OPERATION

FIGURE 8-2:

EXTERNAL CLOCK INPUT

OPERATION

8.2

Configuration Bits

The configuration bits can be either programmed (read

as ‘0’) or unprogrammed (read as ‘1’) to select various

device configurations. These bits are mapped in

program memory location 2007h. The configuration

belongs to the special test/configuration memory space

(2000h-3FFFh) that can be accessed only during

programming.

8.3

Oscillator Configurations

Four different oscillator modes may be selected. The

user

can

program

two

configuration

bits

(FOSC1:FOSC0) in the CONFIG register to select one of

these modes:

• LP = Low-Power Crystal

• XT = Crystal/Resonator

• HS = High-speed Crystal Resonator

In all modes, a crystal or ceramic resonator is

connected to the OSC1/CLKIN and OSC2/CLKOUT

pins to establish oscillation (Figure 8-1). The oscillator

design requires the use of a parallel-cut crystal. The

device can also have an external clock source to drive

the OSC1/CLKIN pin (Figure 8-2).

The device will default to HS mode if the CONFIG

SLEEP

TO INTERNAL

LOGIC

OSC1

OSC2

XTAL

MCP2505X

OSC1

MCP2505X

Open

Clock from

ext. System

OSC2

MCP25020I/P Datasheet(PDF) 47 Page - Microchip Technology

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