DEVICE OVERVIEW
This document contains device specific information for the following devices: This family offers the advantages of all PIC18 micro controllers – namely, high computational performance at an economical price – with the addition of high endurance, Enhanced Flash program memory. On top of these features, the PIC18F4321 family introduces design enhancements that make these microcontrollers a logical choice for many high-performance, power sensitive applications.

• PIC18F2221 • PIC18LF2221
• PIC18F2321 • PIC18LF2321
• PIC18F4221 • PIC18LF4221
• PIC18F4321 • PIC18LF4321

New Core Features
nanoWatt TECHNOLOGY
All of the devices in the PIC18F4321 family incorporate a range of features that can significantly reduce power consumption during operation. Key items include:
• Alternate Run Modes:By clocking the controller from the Timer1 source or the internal oscillator
block, power consumption during code execution can be reduced by as much as 90%.
• Multiple Idle Modes:The controller can also run with its CPU core disabled but the peripherals still active. In these states, power consumption can be reduced even further, to as little as 4% of normal operation requirements.
• On-the-Fly Mode Switching:The power-managed modes are invoked by user code during operation, allowing the user to incorporate power-saving ideas into their application’s software design.
• Low Consumption in Key Modules: The power requirements for both Timer1 and the Watchdog Timer are minimized. See Section 26.0 “Electrical Characteristics” for values.

MULTIPLE OSCILLATOR OPTIONS AND FEATURES
All of the devices in the PIC18F4321 family offer ten different oscillator options, allowing users a wide range of choices in developing application hardware. These include:
• Four Crystal modes, using crystals or ceramic resonators.
• Two External Clock modes, offering the option of using two pins (oscillator input and a divide-by-4 clock output) or one pin (oscillator input, with the second pin reassigned as general I/O).
• Two External RC Oscillator modes with the same pin options as the External Clock modes.
• Two Internal Oscillator modes which provide an 8 MHz clock and an INTRC source
(approximately 31 kHz), as well as a range of 6 user-selectable clock frequencies, between
125 kHz to 4 MHz, for a total of 8 clock frequencies. One or both of the oscillator pins can be used for general purpose I/O.
• A Phase Lock Loop (PLL) frequency multiplier, available to both the high-speed crystal and
internal oscillator modes, which allows clock speeds of up to 40 MHz. Used with the internal
oscillator, the PLL gives users a complete selection of clock speeds, from 31 kHz to 32 MHz – all
without using an external crystal or clock circuit. Besides its availability as a clock source, the internal oscillator block provides a stable reference source that gives the family additional features for robust operation:
• Fail-Safe Clock Monitor:This option constantly monitors the main clock source against a reference signal provided by the internal oscillator. If a clock failure occurs, the controller is switched to the internal oscillator block, allowing for continued low-speed operation or a safe application shutdown.
• Two-Speed Start-up:This option allows the internal oscillator to serve as the clock source
from Power-on Reset, or wake-up from Sleep mode, until the primary clock source is available.