Microchip Technology MA160014 Data Sheet

 2010-2012 Microchip Technology Inc.

DS41412F-page 355

PIC18(L)F2X/4XK22 devices include several features
intended to maximize reliability and minimize cost through
elimination of external components. These are:

• Oscillator Selection

• Resets:

- Power-on Reset (POR)

- Power-up Timer (PWRT)

- Oscillator Start-up Timer (OST)

- Brown-out Reset (BOR)

• Interrupts

• Watchdog Timer (WDT)

• Code Protection

• ID Locations

• In-Circuit Serial Programming™

The oscillator can be configured for the application
depending on frequency, power, accuracy and cost. All
of the options are discussed in detail in 

A complete discussion of device Resets and interrupts
is available in previous sections of this data sheet.

In addition to their Power-up and Oscillator Start-up
Timers provided for Resets, PIC18(L)F2X/4XK22
devices have a Watchdog Timer, which is either
permanently enabled via the Configuration bits or
software controlled (if configured as disabled).

The inclusion of an internal RC oscillator also provides
the additional benefits of a Fail-Safe Clock Monitor
(FSCM) and Two-Speed Start-up. FSCM provides for
background monitoring of the peripheral clock and
automatic switchover in the event of its failure. Two-
Speed Start-up enables code to be executed almost
immediately on start-up, while the primary clock source
completes its start-up delays. 

All of these features are enabled and configured by
setting the appropriate Configuration register bits.

The Configuration bits can be programmed (read as
‘0’) or left unprogrammed (read as ‘1’) to select various
device configurations. These bits are mapped starting
at program memory location 300000h.

The user will note that address 300000h is beyond the
user program memory space. In fact, it belongs to the
configuration memory space (300000h-3FFFFFh), which
can only be accessed using table reads and table writes.

Programming the Configuration registers is done in a
manner similar to programming the Flash memory. The
WR bit in the EECON1 register starts a self-timed write
to the Configuration register. In Normal operation
mode, a TBLWT instruction with the TBLPTR pointing to
the Configuration register sets up the address and the
data for the Configuration register write. Setting the WR
bit starts a long write to the Configuration register. The
Configuration registers are written a byte at a time. To
write or erase a configuration cell, a TBLWT instruction
can write a ‘1’ or a ‘0’ into the cell. For additional details
on Flash programming, refer to