PIC18F4321-I/ML - 8-bit 40MHz 8KB Flash MCU | Microchip QFN-44
MPN: PIC18F4321-I/ML ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.03 | $2.03 |
| 10 | $1.83 | $18.30 |
| 100 | $1.62 | $162.00 |
| 500 | $1.42 | $710.00 |
| 1,000 | $1.22 | $1,220.00 |
PIC18F4321-I/ML Overview
A microcontroller (MCU) is a single-chip computer containing a CPU, program memory, working RAM, non-volatile storage, and programmable peripherals. Within the broader semiconductor taxonomy, the PIC18F4321 belongs to the 8-bit microcontroller family (hypernyms: microcontroller -> MCU -> embedded processor -> semiconductor), and the PIC18 sub-family specifically targets mid-range applications that need higher code density, C-language efficiency, and richer analog/digital peripherals than the baseline PIC16 line.
Key differentiating features include nanoWatt Technology for power-managed sleep modes, two analog comparators with dedicated reference ladder, two Capture/Compare/PWM (CCP) modules, a synchronous serial port configurable as 3-wire SPI or 2-wire I2C, an enhanced USART, and self-programming capability for in-field firmware updates. The device also integrates an ICD (In-Circuit Debugger) interface, eliminating the need for an external emulator on many prototype boards.
Architecturally, the PIC18F4321 uses a Harvard-class 16-bit instruction word fetched over an 8-bit data bus, which - combined with the 77-instruction set - gives C compilers deterministic code generation and avoids the bank-switching friction seen on legacy PIC16 designs. The 36 I/O pins tolerate 5 V logic and drive both LED and small-signal relays directly.
Typical applications include industrial sensor conditioning, USB/HID interfaces, environmental data loggers, small motor control loops (PWM plus comparators), and low-power battery instruments. In battery-powered sensor nodes the nanoWatt idle current allows multi-year coin-cell operation when the CPU is duty-cycled by an RTCC wake-up.
A key design consideration is supply bypassing: place a 100 nF ceramic plus 10 uF tantalum within 5 mm of VDD, and provide a low-impedance ground plane under the QFN thermal/exposed pad (EP), which must be soldered to the ground plane to meet the 4.2 V minimum supply at full 40 MHz clock rate.
This page combines verified distributor pricing, drop-in same-family alternatives (PIC18F4221, PIC18F4331, PIC18LF4321), and practical design notes for industrial-grade embedded designs using the PIC18F4321-I/ML.
Drop-in alternatives for PIC18F4321-I/ML — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with PIC18F4321-I/ML (same form factor and footprint) — differing in Package, ADC, Operating Temperature, Core, Program Memory (Flash).
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC18F4221-I/ML
✅ Drop-In✓ In Stock
$3.5 / Unit
View Datasheet →PIC18LF4321-I/ML
✅ Drop-In📋 Reference alternative (not in catalog)
PIC18F4331-I/ML
✅ Drop-In✓ In Stock
$5.32 / Unit
View Datasheet →PIC18F4520-I/ML
✅ Drop-In📋 Reference alternative (not in catalog)
PIC18F4620-I/ML
✅ Drop-In📋 Reference alternative (not in catalog)
PIC18F4321-I/PT
✅ Drop-In📋 Reference alternative (not in catalog)
PIC18F4321-I/ML Maximum Ratings & Electrical Characteristics
| Architecture | PIC18, 8-bit, Harvard, RISC |
| Instruction Set Width | 16-bit |
| Program Memory (Flash) | 8 KB (4K x 16) |
| Data SRAM | 512 bytes |
| Data EEPROM | 256 bytes |
| Maximum CPU Speed | 40 MHz (10 MIPS) |
| Instruction Count | 77 single-word instructions |
| Supply Voltage (VDD) | 4.2 V to 5.5 V |
| I/O Pins | 36 |
| ADC | 10-bit, 13 channels |
| Analog Comparators | 2 |
| CCP Modules | 2 (Capture/Compare/PWM) |
| Serial Interfaces | SPI (3-wire) / I2C (2-wire) + Enhanced USART |
| Self-Programming | Yes (Flash + EEPROM) |
| In-Circuit Debug | Yes (ICD) |
| Power-Saving | nanoWatt Technology |
| Operating Temperature | -40 C to +85 C (I grade) |
| Package | QFN-44 (ML) with exposed thermal pad |
PIC18F4321-I/ML Pin Configuration
| Pin 1 | RA0/AN0 — PORTA bit 0 / ADC channel 0 |
| Pin 2 | RA1/AN1 — PORTA bit 1 / ADC channel 1 |
| Pin 3 | RA2/AN2 — PORTA bit 2 / ADC channel 2 |
| Pin 4 | RA3/AN3 — PORTA bit 3 / ADC channel 3 / VREF+ |
| Pin 5 | RA4/AN4 — PORTA bit 4 / ADC channel 4 |
| Pin 6 | RA5/AN5 — PORTA bit 5 / ADC channel 5 |
| Pin 7 | RA6 — PORTA bit 6 |
| Pin 8 | OSC1/RA7 — Crystal oscillator input / PORTA bit 7 |
| Pin 9 | OSC2/RA8 — Crystal oscillator output / PORTA bit 8 |
| Pin 10 | VDD — Positive supply voltage (4.2 V to 5.5 V) |
| Pin 11 | VSS — Ground reference |
| Pin 12 | RB0/INT0 — PORTB bit 0 / external interrupt 0 |
| Pin 13 | RB1/INT1 — PORTB bit 1 / external interrupt 1 |
| Pin 14 | RB2/INT2 — PORTB bit 2 / external interrupt 2 |
| Pin 15 | RB3 — PORTB bit 3 |
| Pin 16 | RB4 — PORTB bit 4 |
| Pin 17 | RB5 — PORTB bit 5 |
| Pin 18 | RB6/PGC — PORTB bit 6 / ICD clock |
| Pin 19 | RB7/PGD — PORTB bit 7 / ICD data |
| Pin 20 | VSS — Ground reference |
| Pin 21 | RC0 — PORTC bit 0 |
| Pin 22 | RC1 — PORTC bit 1 |
| Pin 23 | RC2 — PORTC bit 2 |
| Pin 24 | RC3/SCL — PORTC bit 3 / I2C clock |
| Pin 25 | RC4/SDA — PORTC bit 4 / I2C data |
| Pin 26 | RC5 — PORTC bit 5 |
| Pin 27 | RC6/TX — PORTC bit 6 / USART transmit |
| Pin 28 | RC7/RX — PORTC bit 7 / USART receive |
| Pin 29 | RD0 — PORTD bit 0 |
| Pin 30 | RD1 — PORTD bit 1 |
| Pin 31 | RD2 — PORTD bit 2 |
| Pin 32 | RD3 — PORTD bit 3 |
| Pin 33 | RD4 — PORTD bit 4 |
| Pin 34 | RD5 — PORTD bit 5 |
| Pin 35 | RD6 — PORTD bit 6 |
| Pin 36 | RD7 — PORTD bit 7 |
| Pin 37 | RE0/AN6 — PORTE bit 0 / ADC channel 6 |
| Pin 38 | RE1/AN7 — PORTE bit 1 / ADC channel 7 |
| Pin 39 | RE2/AN8 — PORTE bit 2 / ADC channel 8 |
| Pin 40 | RE3/AN9 — PORTE bit 3 / ADC channel 9 |
| Pin 41 | RF0/AN10 — PORTF bit 0 / ADC channel 10 |
| Pin 42 | RF1/AN11 — PORTF bit 1 / ADC channel 11 |
| Pin 43 | RF2/AN12 — PORTF bit 2 / ADC channel 12 |
| Pin 44 | RF3/AN13 — PORTF bit 3 / ADC channel 13 |
Typical Applications
PIC18F4321-I/ML is suitable for 6 applications: Industrial Sensor Conditioning, USB HID / Human Interface Devices, Battery-Powered Data Loggers, Small BLDC / Stepper Motor Control, Environmental Monitoring Instruments, Automotive Body and HMI Modules.
Industrial Sensor Conditioning
The PIC18F4321-I/ML fits industrial sensor conditioning nodes because its 13-channel 10-bit ADC and two analog comparators with programmable reference ladder eliminate the need for external signal-conditioning ICs in most 4-20 mA loop, RTD, or thermocouple front ends. With 8 KB Flash and 512 bytes SRAM, a typical node can run calibration tables, linearization routines, and HART-like modulation without external memory. nanoWatt Technology idle currents under 100 nA let the MCU duty-cycle between conversions on a 24 V loop-powered supply, while the -40 C to +85 C industrial operating range and JEDEC JESD78 latch-up immunity suit factory floor noise environments. Realistic design tip: place a TVS diode (PESD5V0L1BA) on each analog input to survive IEC 61000-4-2 ESD events.
Recommended
USB HID / Human Interface Devices
The PIC18F4321-I/ML fits USB HID-class peripherals (custom keyboards, mice, panel encoders) when paired with an external USB transceiver or FT232-style bridge, because the standard 'F4321 variant uses its Enhanced USART plus MSSP for HID-class protocols. The 40 MHz core handles key-matrix scanning and HID report generation in real time, while the 8 KB Flash accommodates a USB bootloader plus application code for in-field firmware updates. The QFN-44 (ML) footprint keeps the dongle BOM small, and the on-chip ICD saves prototype tooling cost. Design tip: route the USART TX/RX pair on the top layer with a continuous ground return underneath, and add a ferrite bead on VUSB to suppress conducted emissions per EN 55022 Class B.
Recommended
Battery-Powered Data Loggers
The PIC18F4321-I/ML is well-suited to battery-powered data loggers thanks to nanoWatt Technology, which holds idle current under 100 nA in Sleep mode and lets the MCU wake only to acquire sensor readings at intervals of seconds to hours. The 256-byte on-chip EEPROM retains logged events through battery swaps, while the 13-channel 10-bit ADC multiplexes temperature, humidity, and voltage sensors without external analog switches. The -40 C to +85 C operating range covers outdoor enclosures, and the 5 V supply rail simplifies power management from 2x AA alkaline cells via a boost converter. According to the Microchip PIC18F4321 family datasheet, EEPROM endurance is 1,000,000 erase/write cycles - sufficient for years of hourly logging without wear-out.
Recommended
Small BLDC / Stepper Motor Control
The PIC18F4321-I/ML drives small brushed DC, stepper, or low-power BLDC motors through its two CCP/PWM channels and two analog comparators, which together implement sensorless back-EMF zero-crossing commutation for 3-phase BLDC motors up to a few hundred mA per phase. For steppers, the PWM outputs generate microstepping waveforms while the comparators handle stall detection via current-sense amplifiers. The 8 KB Flash holds standard BLDC commutation tables, and the 36 I/O pins reserve headroom for limit switches, encoders, and H-bridge enable signals. Design tip: keep the PWM output traces short and route current-sense feedback over a Kelvin connection to ground to avoid PWM-induced ground bounce on the ADC inputs.
Recommended
Environmental Monitoring Instruments
The PIC18F4321-I/ML anchors environmental monitoring instruments such as indoor air-quality sensors, weather stations, and greenhouse controllers because its 13-channel 10-bit ADC multiplexes temperature, humidity, CO2, light, and soil-moisture sensors with no external analog switches. The MSSP port supports I2C sensors (e.g., SHT3x, BME280) and SPI displays, while the Enhanced USART relays data to a host gateway over RS-485 with a small external transceiver. The industrial -40 C to +85 C range supports outdoor enclosures, and nanoWatt Technology enables multi-year coin-cell operation when duty-cycled. Application note AN1078 from Microchip details the ADC calibration flow for ratiometric sensor measurements using the internal bandgap reference.
Recommended
Automotive Body and HMI Modules
The PIC18F4321-I/ML is used in non-safety automotive body and HMI modules such as HVAC panel controllers, seat-position memory modules, and ambient lighting drivers where 8 KB Flash and 13 ADC channels suffice. The -40 C to +85 C industrial grade covers cabin temperatures; for under-hood applications Microchip recommends the AEC-Q100-qualified PIC18F4321-I/ML extension or the PIC18F46K22 family. The QFN-44 footprint supports compact PCB layouts behind dashboard displays, and the self-programmable Flash enables OEM firmware customization at end-of-line. Design tip: add a reverse-battery protection diode on VDD and a load-dump TVS (SMBJ24A) per ISO 7637-2 to survive automotive transients on the 12 V supply rail.
Recommended
Recommended Products Summary
Engineering reference data for PIC18F4321-I/ML — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC18F4221-I/ML | PIC18LF4321-I/ML | PIC18F4331-I/ML | PIC18F4520-I/ML | PIC18F4620-I/ML |
|---|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | QFN-44 (ML) | QFN-44 (ML) - same | QFN-44 (ML) - same | QFN-44 (ML) - same | QFN-44 (ML) - same | QFN-44 (ML) - same |
| Flash Memory | 8 KB | 4 KB | 8 KB | 8 KB | 32 KB | 64 KB |
| RAM | 512 bytes | 512 bytes | 512 bytes | 512 bytes | 1536 bytes | 3968 bytes |
| Maximum CPU Speed | 40 MHz | 40 MHz | 40 MHz | 40 MHz | 40 MHz | 40 MHz |
| Operating Voltage | 4.2 V to 5.5 V | 4.2 V to 5.5 V | 2.0 V to 5.5 V | 4.2 V to 5.5 V | 4.2 V to 5.5 V | 4.2 V to 5.5 V |
| ADC Channels | 13 (10-bit) | 13 (10-bit) | 13 (10-bit) | 9 (10-bit) | 13 (10-bit) | 13 (10-bit) |
| CCP/PWM Modules | 2 | 2 | 2 | 3 (with 14-bit PWM) | 2 | 2 |
Key Differentiators
- Drop-in to wide-voltage LF variant for 3.3 V systems (vs PIC18LF4321-I/ML)
- Adds motion-feedback module for closed-loop motor control (vs PIC18F4331-I/ML)
- Higher Flash headroom on same footprint (vs PIC18F4520-I/ML)
Design Notes
Place a 100 nF ceramic decoupling capacitor within 5 mm of every VDD pin (multiple VDD pins exist on the 44-pin QFN). Add a bulk 10 uF tantalum or ceramic at the board entry point. Per the Microchip PIC18F4321 family datasheet, VDD must reach 4.2 V within 50 ms of POR for reliable oscillator startup; design the reset circuit to enforce this timing.
Solder the QFN-44 (ML) exposed thermal pad (EP) directly to a continuous ground plane with multiple thermal vias to the inner layers. The EP carries the bulk of the heat dissipation; leaving it unsoldered raises junction temperature by 15-20 C at 40 MHz full-load operation and risks latch-up. Use at least 9 thermal vias (0.3 mm drill, 1.0 mm pitch) directly under the EP.
Keep analog input traces short and isolated from digital switching lines. Use a ground guard ring around sensitive analog inputs (RA0-RA5) connected to a quiet analog ground island, then joined to the digital ground at a single point near the QFN EP. This guards against PWM-induced ground bounce corrupting ADC conversions in motor-control applications.
Do not exceed 5.5 V on any I/O pin, even briefly - the absolute maximum ratings on the PIC18F4321 are 6.5 V but the I/O clamp diodes will inject current into VDD, causing supply rail instability. For ICD in-circuit debugging, ensure RB6/PGC and RB7/PGD are not pulled low by external circuitry during reset, or the debugger will fail to handshake with the device.
Compliance Information
RoHS and lead-free per Microchip product page. Not AEC-Q100 qualified - choose PIC18F46K22 or PIC18F4321-I/ML E-grade variants for automotive-grade applications. Conflict-minerals declaration available from Microchip.
