PIC18F4321T-I/ML - 8KB Flash 8-bit MCU 40MHz QFN-44 | Microchip
MPN: PIC18F4321T-I/ML ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.4 | $6.40 |
| 10 | $5.78 | $57.80 |
| 100 | $5.15 | $515.00 |
| 500 | $4.62 | $2,310.00 |
| 1,000 | $4.1 | $4,100.00 |
PIC18F4321T-I/ML Overview
An 8-bit microcontroller (MCU) is a programmable integrated circuit that executes instructions from on-chip program memory while interacting with peripherals through digital and analog I/O pins. The PIC18F family sits above PIC16 in Microchip's 8-bit hierarchy, offering enhanced peripherals and nanoWatt power management. Architecturally, an 8-bit MCU typically includes a CPU core, Flash program memory, SRAM for data, EEPROM for non-volatile storage, timers, ADC, communication peripherals, and GPIO. PIC18F devices extend the baseline PIC16 instruction set with 16-bit instructions and a hardware multiplier for C-friendly code generation.
The PIC18F4321 features 36 digital I/O pins, a 10-bit ADC with multiple channels, multiple capture/compare/PWM modules, USART, MSSP (I2C/SPI), and nanoWatt Technology power management for sleep/idle modes. The 44-pin VQFN exposed-pad package provides a compact footprint and a thermal dissipation path for the silicon die through the EP.
This microcontroller is well suited for industrial control nodes, sensor signal conditioning, motor control, low-power battery devices, and consumer appliances where the PIC18 ecosystem of MPLAB X, XC8 compiler, and a broad library of code examples reduces time-to-market. The device is also a strong candidate for legacy PIC18F4321 designs migrating from PDIP to a smaller QFN footprint.
In designs, ensure the exposed pad is soldered to a sufficient copper pour for thermal dissipation, and follow Microchip's QFN land-pattern guidelines. The ICSP programming pins must remain accessible for in-circuit programming and debugging.
Drop-in alternatives for PIC18F4321T-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 PIC18F4321T-I/ML (same form factor and footprint) — differing in ADC, Package, I/O Pins, Maximum CPU Speed, Operating Temperature.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC18F4321-I/ML
✅ Drop-In✓ In Stock
$1.22 / Unit
View Datasheet →PIC18F4321T-I/ML Maximum Ratings & Electrical Characteristics
| Family | PIC18F |
| Core | 8-bit PIC |
| Program Memory Type | Flash |
| Program Memory Size | 8 KB (4K x 16) |
| RAM Size | 512 bytes |
| EEPROM Size | 256 bytes |
| Maximum CPU Speed | 40 MHz |
| Performance | 10 MIPS |
| Instruction Execution Time | 100 ns (at 40 MHz) |
| Number of I/O Pins | 36 |
| Supply Voltage Range | 2.0 V to 5.5 V |
| ADC | 10-bit |
| Operating Temperature Range | -40 C to +85 C (Industrial) |
| Package | 44-pin VQFN (8x8 mm) with exposed pad |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
PIC18F4321T-I/ML Pin Configuration
| Pin 1 | NC — Not connected |
| Pin 2 | RA0/AN0 — Digital I/O / Analog input channel 0 |
| Pin 3 | RA1/AN1 — Digital I/O / Analog input channel 1 |
| Pin 4 | RA2/AN2/VREF- — Digital I/O / Analog input channel 2 / ADC VREF- |
| Pin 5 | RA3/AN3/VREF+ — Digital I/O / Analog input channel 3 / ADC VREF+ |
| Pin 6 | RA4/T0CKI — Digital I/O / Timer0 clock input |
| Pin 7 | RA5/AN4/SS — Digital I/O / Analog input channel 4 / SPI slave select |
| Pin 8 | OSC1/CLKI/RA7 — Oscillator input / External clock / Digital I/O |
| Pin 9 | OSC2/CLKO/RA6 — Oscillator output / Clock out / Digital I/O |
| Pin 10 | RC0/T1OSO/T1CKI — Digital I/O / Timer1 oscillator output / clock input |
| Pin 11 | RC1/T1OSI/CCP2 — Digital I/O / Timer1 oscillator input / CCP2 |
| Pin 12 | RC2/CCP1 — Digital I/O / CCP1 PWM output |
| Pin 13 | RC3/SCK/SCL — Digital I/O / SPI clock / I2C clock |
| Pin 14 | RC4/SDI/SDA — Digital I/O / SPI data in / I2C data |
| Pin 15 | RC5/SDO — Digital I/O / SPI data out |
| Pin 16 | RC6/TX/CK — Digital I/O / USART TX / clock |
| Pin 17 | RC7/RX/DT — Digital I/O / USART RX / data |
| Pin 18 | VSS — Ground reference |
| Pin 19 | VDD — Positive supply voltage 2.0V to 5.5V |
| Pin 20 | RB0/INT0/FLT0 — Digital I/O / External interrupt 0 / PWM fault |
| Pin 21 | RB1/INT1 — Digital I/O / External interrupt 1 |
| Pin 22 | RB2/INT2 — Digital I/O / External interrupt 2 |
| Pin 23 | RB3/INT3/CCP2 — Digital I/O / External interrupt 3 / CCP2 |
| Pin 24 | RB4/KBI0 — Digital I/O / Keyboard interrupt 0 |
| Pin 25 | RB5/KBI1 — Digital I/O / Keyboard interrupt 1 |
| Pin 26 | RB6/KBI2/PGC — Digital I/O / Keyboard interrupt 2 / ICSP clock |
| Pin 27 | RB7/KBI3/PGD — Digital I/O / Keyboard interrupt 3 / ICSP data |
| Pin 28 | MCLR/VPP/RE3 — Master clear reset / Programming voltage / Digital I/O |
| Pin 29 | RD0 — Digital I/O |
| Pin 30 | RD1 — Digital I/O |
| Pin 31 | RD2 — Digital I/O |
| Pin 32 | RD3 — Digital I/O |
| Pin 33 | RD4 — Digital I/O |
| Pin 34 | RD5 — Digital I/O |
| Pin 35 | RD6 — Digital I/O |
| Pin 36 | RD7 — Digital I/O |
| Pin 37 | VSS — Ground reference |
| Pin 38 | VDD — Positive supply voltage |
| Pin 39 | RE0/RD — Digital I/O |
| Pin 40 | RE1/WR — Digital I/O |
| Pin 41 | RE2/CS — Digital I/O |
| Pin 42 | AVDD — Analog supply voltage |
| Pin 43 | AVSS — Analog ground reference |
| Pin 44 | EP — Exposed pad - thermal dissipation, solder to ground plane |
Typical Applications
PIC18F4321T-I/ML is suitable for 6 applications: Industrial Sensor Interface Node, Battery-Powered Remote Control / IoT Edge Node, Consumer Appliance Control Board, Automotive Aftermarket Accessory (Non-Safety), Educational and Maker Embedded Platform, Motor Drive and PWM Control.
Industrial Sensor Interface Node
The PIC18F4321T-I/ML fits industrial sensor nodes because of its 36 digital I/O pins, 10-bit ADC, and nanoWatt Technology sleep modes. Place the QFN on a board with a copper pour tied to the exposed pad to dissipate heat from the industrial -40C to +85C operating range; the 10 MIPS CPU can sample multiple analog sensors and run a Modbus RTU stack over the USART. Compared with discrete op-amp + ADC chains, this MCU integrates all conversion and signal conditioning in a single 8x8 mm package.
Recommended
Battery-Powered Remote Control / IoT Edge Node
The PIC18F4321T-I/ML's nanoWatt Technology enables Sleep currents in the microampere range, allowing battery-powered IoT edge nodes to run for years on a single coin cell. The 8KB Flash comfortably fits MQTT-SN, BLE beacon drivers, or LoRaWAN stack fragments; the 512B RAM supports small buffers. Operating from 2.0V to 5.5V, it accepts direct battery input without an LDO. Designers should exploit the MSSP (I2C/SPI) ports to attach sensors and the USART for host-side debug.
Recommended
Consumer Appliance Control Board
The PIC18F4321T-I/ML integrates 36 I/O lines plus USART and MSSP, making it suitable for white-goods, HVAC, and kitchen-appliance control boards. The 8KB Flash stores the appliance state machine and user-interface firmware; the 256B EEPROM retains settings across power cycles. Its 40 MHz / 10 MIPS throughput handles triac-zero-crossing control, keypad scanning, and sensor fusion in real time, while the 5V operation directly drives relay and triac interfaces.
Recommended
Automotive Aftermarket Accessory (Non-Safety)
The PIC18F4321T-I/ML's industrial -40C to +85C range covers cabin and non-safety automotive accessory conditions. The 36 I/O lines and 10-bit ADC support dashboard lighting controllers, mirror controllers, and body-electronics accessories; the MSSP interfaces with SPI/I2C peripherals. Note that AEC-Q100 is not qualified, so it cannot replace safety-critical components, but it is fully appropriate for non-safety accessories.
Recommended
Educational and Maker Embedded Platform
The PIC18F4321T-I/ML is popular in academic labs and maker projects because of the free MPLAB X IDE, XC8 compiler, and PICkit programmer support. With 36 I/O lines, students can drive LEDs, character LCDs, servo motors, and UART peripherals from a single chip. The 44-pin QFN footprint teaches surface-mount soldering skills, while ICSP enables in-circuit debugging and step-through learning.
Recommended
Motor Drive and PWM Control
The PIC18F4321T-I/ML's Capture/Compare/PWM (CCP) modules and enhanced 16-bit timers generate precise PWM signals for DC motor speed control and brushless-DC commutation. The 10 MIPS throughput executes field-oriented control loops at modest RPMs, and the 36 I/O lines drive gate-driver enable signals. The industrial -40C to +85C temperature range supports enclosed motor housings; pair the QFN exposed pad with a copper pour for thermal relief.
Recommended
Recommended Products Summary
Engineering reference data for PIC18F4321T-I/ML — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC18F4321-I/ML | PIC18F4320T-I/PT | PIC18F4320-I/PT |
|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 44-pin VQFN (8x8) with EP | 44-pin VQFN (8x8) with EP | 44-pin TQFP | 44-pin TQFP |
| Program Memory | 8 KB Flash | 8 KB Flash | 8 KB Flash | 8 KB Flash |
| RAM | 512 bytes | 512 bytes | 512 bytes | 512 bytes |
| Maximum CPU Speed | 40 MHz | 40 MHz | 40 MHz | 40 MHz |
| Number of I/O Pins | 36 | 36 | 36 | 36 |
| Supply Voltage Range | 2.0V to 5.5V | 2.0V to 5.5V | 2.0V to 5.5V | 2.0V to 5.5V |
| Operating Temperature | -40C to +85C (Industrial) | -40C to +85C | -40C to +85C | -40C to +85C |
| Packaging Media | Tape & Reel | Tray | Tape & Reel | Tray |
Key Differentiators
- Industrial -40C to +85C temperature range in compact QFN-44 (vs PIC18F4320T-I/PT)
- Same die and pinout, tape-and-reel packaging optimized for high-volume assembly (vs PIC18F4321-I/ML)
- Established PIC18 ecosystem with 8KB Flash and nanoWatt technology (vs PIC18F4221T-I/ML)
Design Notes
The PIC18F4321T-I/ML's 44-pin VQFN exposed pad must be soldered to a copper pour for both electrical ground and thermal dissipation. At 40 MHz worst-case operation in industrial temperature, the device stays within junction ratings with a 1-2 square inch copper pour. For high ambient temperature environments, increase the pour area or add thermal vias to inner planes.
Use Microchip's recommended QFN-44 land pattern. Keep digital traces short, place decoupling capacitors (100 nF + 10 uF) within 5 mm of each VDD pin, and route the AVSS/AVDD pair separately from digital VDD/VSS to minimize ADC noise coupling. The exposed pad should connect to the ground plane through at least 4 thermal vias.
Route the ICSP PGC/PGD lines away from switching nodes and noisy power traces to ensure reliable in-circuit programming. Place an RC filter on MCLR if the system has long MCLR traces. Group the USART TX/RX differential-style routing together, and isolate the analog AVSS/AVDD pins from noisy digital traces to preserve ADC accuracy.
Do not exceed 5.5V on any VDD or digital I/O pin; the PIC18F4321 is not 5V-tolerant when powered at 3.3V. Always honor the brown-out-reset voltage settings in CONFIG to ensure clean reset behavior. The ADC's acquisition time depends on the source impedance - add a buffer for high-impedance sensors.
Compliance Information
RoHS compliant per Microchip product page. Industrial temperature grade -40C to +85C; not AEC-Q100 qualified for automotive safety applications. Lead-free (Pb-free) reflow profile per Microchip datasheet.
