2007 Microchip Technology Inc.
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
register is actually beyond program memory space and
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
design requires the use of a parallel-cut crystal. The
device can also have an external clock source to drive
The device will default to HS mode if the CONFIG
register is not programmed.
SLEEP
TO INTERNAL
LOGIC
C1
C2
OSC1
OSC2
XTAL
RF
MCP2505X
OSC1
MCP2505X
Open
Clock from
ext. System
OSC2