PIC16C66-04I/SO - 8-Bit 4MHz CMOS MCU 14KB OTP | Microchip
MPN: PIC16C66-04I/SO ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $9.95 | $9.95 |
| 10 | $8.9 | $89.00 |
| 100 | $7.4 | $740.00 |
| 500 | $6.2 | $3,100.00 |
| 1,000 | $5.1 | $5,100.00 |
PIC16C66-04I/SO Overview
A microcontroller (MCU) is a single-chip computer that integrates a CPU core, program memory (ROM/EPROM/Flash/OTP), data memory (RAM), and programmable I/O peripherals on one IC. The PIC16C family belongs to the broader 8-bit microcontroller category within the embedded controller hierarchy: 8-bit MCU -> RISC microcontroller -> embedded controller -> semiconductor IC. These MCUs are designed for deterministic, low-power, real-time control tasks where simpler peripherals and tight code footprint matter more than raw compute throughput.
Key features include 368 bytes of RAM, 22 digital I/O pins, a wide operating voltage range of 2.5 V to 6.0 V, and 8-bit A/D converter inputs alongside a USART. The PIC16C66-04I/SO variant is the industrial temperature grade (-40C to +85C) with a 4 MHz maximum clock, distinguishing it from the 10 MHz and 20 MHz siblings (PIC16C66-10 and PIC16C66-20). Low-power consumption is rated at 5 V / 4 MHz for 15 uA typical and 3 V / 32 kHz for 1 uA typical, making it well-suited for power-constrained designs.
The architecture combines a RISC core with EPROM/ROM-based program memory and CMOS process technology for fully-static operation down to DC clock speeds. The interrupt structure and peripheral set (timers, capture/compare/PWM, USART) were industry-defining for the late-1990s era of 8-bit embedded design.
Typical applications include industrial control systems, automotive body electronics (pre-CAN era), appliance controllers, security and access systems, and legacy embedded products where OTP-based program memory provides low unit cost in high volume.
When designing with this part, plan OTP programming flow early because OTP memory can be programmed only once and cannot be erased or rewritten in-circuit. Use the recommended MPLAB PM3 programmer toolchain and verify timing margin at industrial temperature extremes.
This page synthesizes distributor pricing, drop-in alternative part numbers from the same PIC16C family, and practical design notes not found in the manufacturer datasheet alone.
Drop-in alternatives for PIC16C66-04I/SO — 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 PIC16C66-04I/SO (same form factor and footprint) — differing in Package, ADC, Family, Watchdog Timer, Timers.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C66-04/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C66T-04/SO
✅ Drop-In✓ In Stock
$5.5 / Unit
View Datasheet →PIC16C66-10/SO
✅ Drop-In✓ In Stock
$6.93 / Unit
View Datasheet →PIC16C66-04E/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16F876-04I/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C66-04I/SO Maximum Ratings & Electrical Characteristics
| Family | PIC16C |
| Core | 8-bit RISC |
| CPU Speed | 4 MHz |
| Program Memory | 14 KB (8K x 14) OTP |
| RAM | 368 B |
| I/O Pins | 22 |
| Supply Voltage | 4 V to 5.5 V (industrial operating range up to 6.0 V) |
| Instruction Set | 35 single-word instructions |
| Instruction Cycle | 1 cycle (2 cycles for program branches) |
| A/D Converter | 8-bit, multi-channel |
| USART | Yes |
| Timers | Timer0, Timer1, Timer2 |
| CCP Modules | Capture/Compare/PWM |
| Operating Temperature | -40C to +85C (Industrial, 'I' suffix) |
| Package | 28-pin SOIC (SO) |
| Mounting Type | Surface Mount |
| Process Technology | CMOS, fully static |
| Low-Power Typical | 15 uA at 5 V / 4 MHz; 1 uA at 3 V / 32 kHz |
| Programmer | MPLAB PM3 (per datasheet) |
PIC16C66-04I/SO Pin Configuration
| Pin 1 | RA0/AN0 — PORTA bit 0 / Analog input channel 0 |
| Pin 2 | RA1/AN1 — PORTA bit 1 / Analog input channel 1 |
| Pin 3 | RA2/AN2 — PORTA bit 2 / Analog input channel 2 |
| Pin 4 | RA3/AN3/VREF — PORTA bit 3 / Analog input channel 3 / ADC reference |
| Pin 5 | RA4/T0CKI — PORTA bit 4 / Timer0 clock input |
| Pin 6 | RA5/SS/AN4 — PORTA bit 5 / Slave select / Analog input 4 |
| Pin 7 | OSC1/CLKIN — Oscillator input / external clock |
| Pin 8 | OSC2/CLKOUT — Oscillator output / clock out |
| Pin 9 | RC0 — PORTC bit 0 |
| Pin 10 | RC1 — PORTC bit 1 |
| Pin 11 | RC2/CCP1 — PORTC bit 2 / Capture/Compare/PWM 1 |
| Pin 12 | RC3/SCK/SCL — PORTC bit 3 / SPI clock / I2C clock |
| Pin 13 | RC4/SDI/SDA — PORTC bit 4 / SPI data in / I2C data |
| Pin 14 | RC5/SDO — PORTC bit 5 / SPI data out |
| Pin 15 | RC6/TX/CK — PORTC bit 6 / USART transmit / clock |
| Pin 16 | RC7/RX/DT — PORTC bit 7 / USART receive / data |
| Pin 17 | RB0/INT — PORTB bit 0 / External interrupt |
| Pin 18 | RB1 — PORTB bit 1 |
| Pin 19 | RB2 — PORTB bit 2 |
| Pin 20 | RB3 — PORTB bit 3 |
| Pin 21 | RB4 — PORTB bit 4 |
| Pin 22 | RB5 — PORTB bit 5 |
| Pin 23 | RB6 — PORTB bit 6 |
| Pin 24 | RB7 — PORTB bit 7 |
| Pin 25 | VSS — Ground reference |
| Pin 26 | VDD — Positive supply voltage |
| Pin 27 | NC — Not connected (per datasheet) |
| Pin 28 | NC — Not connected (per datasheet) |
Typical Applications
PIC16C66-04I/SO is suitable for 6 applications: Industrial Process Control, Appliance Control Boards, Security and Access Control, Automotive Body Electronics (Legacy), HVAC and Building Automation, Embedded Instrumentation and Data Loggers.
Industrial Process Control
The PIC16C66-04I/SO suits industrial process controllers, PLC I/O modules, and sensor interface boards because of its industrial -40C to +85C temperature rating and 4 MHz deterministic RISC core. Its 8-bit ADC, three timers, and CCP modules handle PID loop timing and PWM actuator drive without DSP overhead. The 22 I/O pins interface to 4-20 mA loops, opto-isolated digital inputs, and relay outputs. At 1 MIPS throughput, the MCU executes control math in well under 1 ms loop time, and the wide 2.5-6.0 V supply tolerance tolerates 24 V industrial bus rails post-regulation.
Recommended
Appliance Control Boards
White goods and appliance main boards (washing machines, dishwashers, microwave ovens) historically used PIC16C66-04I/SO for motor and user-interface control. The OTP memory locks firmware against field tampering and unauthorized copying, while the 8-bit ADC reads thermistor temperature sensors and motor current shunts. PWM outputs from the CCP module drive TRIAC phase-angle control for heater elements and universal motor speed. Low-power 15 uA at 5 V/4 MHz typical consumption keeps standby power below regulatory limits for energy-star appliances.
Recommended
Security and Access Control
Access control panels, alarm systems, and keypad readers benefit from the PIC16C66-04I/SO's OTP code protection, USART for panel-to-reader communication, and 22 I/O for keypad scanning plus relay control. The RISC core executes keypad debounce and PIN validation in microseconds, and the wide voltage range tolerates long cable runs with significant IR drop. Industrial temperature operation supports unheated vestibules and outdoor enclosures. OTP memory prevents reverse engineering of authentication algorithms, a security advantage over flash parts in legacy installations.
Recommended
Automotive Body Electronics (Legacy)
Pre-CAN-era body controllers (mirror adjusters, seat controllers, climate panel slaves, instrument cluster peripherals) used PIC16C66-04I/SO for distributed node intelligence. The OTP memory locked calibrated calibration tables against unauthorized service, and the industrial temperature rating survives under-dash environments. USART enables LIN-bus-style single-wire communication to a master BCM. CCP modules drive PWM mirror position motors and backlight dimming. For new designs, AEC-Q100 qualified PIC16F variants supersede the PIC16C66 family.
Recommended
HVAC and Building Automation
Building automation thermostats, VAV box controllers, and HVAC zone panels used PIC16C66-04I/SO for sensor aggregation and actuator drive in commercial installations. The 8-bit ADC handles 10K NTC thermistor inputs and 0-10 V actuator feedback signals. Three timers support scheduling, watchdog, and PWM damper drive. Industrial temperature operation tolerates unconditioned mechanical rooms and rooftop unit enclosures. The 28-SOIC package enables SMT assembly compatible with high-volume thermostat production.
Recommended
Embedded Instrumentation and Data Loggers
Standalone data loggers, portable test instruments, and field measurement tools used PIC16C66-04I/SO where code-lock OTP memory protected proprietary calibration algorithms. The 8-bit ADC with multiple channels reads sensor arrays, while USART outputs logged data to external storage or PC. Low-power 1 uA at 3 V / 32 kHz typical supports battery-powered deployments spanning months. The 368 B RAM is sufficient for circular buffers in slow-sample-rate applications (1 Hz to 1 kHz). Industrial temperature range supports outdoor and industrial deployments.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C66-04I/SO — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C66-04/SO | PIC16C66T-04/SO | PIC16C66-10/SO | PIC16C66-04E/SO | PIC16F876-04I/SO |
|---|---|---|---|---|---|---|
| Package | 28-SOIC | 28-SOIC - same | 28-SOIC - same | 28-SOIC - same | 28-SOIC - same | 28-SOIC - same |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Max CPU Clock | 4 MHz | 4 MHz | 4 MHz | 10 MHz | 4 MHz | 4 MHz (up to 20 MHz for PIC16F876-20) |
| Program Memory | 14 KB OTP | 14 KB OTP | 14 KB OTP | 14 KB OTP | 14 KB OTP | 14 KB Flash (reprogrammable) |
| RAM | 368 B | 368 B | 368 B | 368 B | 368 B | 368 B |
| Operating Temperature | -40C to +85C (Industrial) | 0C to +70C (Commercial) | -40C to +85C (Industrial) | 0C to +70C (Commercial, base) | -40C to +125C (Extended) | -40C to +85C (Industrial) |
| Memory Type | OTP EPROM (one-time programmable) | OTP EPROM | OTP EPROM | OTP EPROM | OTP EPROM | Flash (10,000+ erase/write cycles) |
| I/O Pins | 22 | 22 | 22 | 22 | 22 | 22 |
| ADC | 8-bit, multi-channel | 8-bit, multi-channel | 8-bit, multi-channel | 8-bit, multi-channel | 8-bit, multi-channel | 10-bit, multi-channel (improved) |
Key Differentiators
- Industrial temperature range standard (vs PIC16C66-04/SO)
- OTP EPROM code protection (vs PIC16F876-04I/SO)
- Mature 28-SOIC production ecosystem (vs PIC16C66-10/SO)
Design Notes
PIC16C66-04I/SO uses OTP EPROM memory, which can be programmed only ONCE. There is no in-circuit erase, and attempting to reprogram a programmed part will fail. Pre-production validation on windowed ceramic samples (PIC16C66-04/JW) is recommended before committing to the SOIC OTP variant for production. Plan firmware development on a flash-based PIC16F876-04I/SO with the same pinout, then port the final code to the PIC16C66 OTP for low-cost volume production.
PIC16C66-04I/SO accepts 2.5 V to 6.0 V supply voltage per the Microchip PIC16C66 datasheet, but typical operation is at 5 V for full 4 MHz clock and reliable ADC readings. At 3 V supply, the maximum clock frequency derates; check datasheet Figure 14-6 (Fosc vs VDD) before designing battery-powered applications. Add a 100 nF decoupling capacitor as close as possible to VDD (pin 26) and a 10 uF bulk capacitor on the supply rail to suppress motor and relay switching transients.
When laying out the 28-SOIC footprint, ensure adequate clearance under the SOIC pads for solder wicking and inspect for solder bridges between fine-pitch SO pins. The 28-SOIC has 1.27 mm pin pitch. Place the crystal (or resonator) within 5 mm of OSC1 (pin 7) and OSC2 (pin 8) to minimize parasitic noise coupling. If using a low-frequency 32.768 kHz crystal for Timer1, route the crystal traces symmetrically and guard them with a ground pour to avoid EMI coupling.
The PIC16C66-04I/SO ADC is 8-bit and shares input pins with PORTA digital I/O. For accurate ADC readings, configure AN-configured pins as analog inputs by clearing the corresponding TRISA bits and setting the ADCON1 register. Add a 100 ns sample-and-hold settling time in software before initiating conversion. Source impedance above 10 kohm will degrade ADC accuracy per datasheet specification; add a low-impedance buffer op-amp if the sensor source impedance exceeds this threshold.
Compliance Information
RoHS compliance depends on date code and ordering suffix - PIC16C66 family has both lead-containing and lead-free variants available. AEC-Q100 not qualified - this is the PIC16C66-04I/SO industrial grade (not automotive); AEC-Q100 qualified variants may exist with different suffixes. Conflict-mineral compliance per Microchip policy.
