PIC16C66-04/SO - 8-Bit 4MHz OTP MCU 14KB | Microchip
MPN: PIC16C66-04/SO ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.77 | $3.77 |
| 10 | $3.42 | $34.20 |
| 100 | $3.05 | $305.00 |
| 500 | $2.86 | $1,430.00 |
| 1,000 | $2.65 | $2,650.00 |
PIC16C66-04/SO Overview
A microcontroller (MCU) is a single-chip computer that integrates a CPU core, program memory (ROM/Flash/OTP), working memory (RAM), and programmable I/O peripherals. The PIC16C66 belongs to the PIC16C6X mid-range family, which sits in the taxonomy: microcontroller -> embedded controller -> 8-bit MCU -> CMOS RISC MCU -> PIC16 mid-range -> 16C6X family. It offers 35 single-word instructions (RISC architecture) for fast code development and predictable execution timing.
Key features include a wide operating voltage range up to 6.0 V, 22 I/O pins, three timers (Timer0, Timer1, Timer2), a USART for serial communication, and capture/compare/PWM (CCP) peripherals. Low-power consumption is a notable strength: typical 15 µA at 5 V/4 MHz and 1 µA at 3 V/32 kHz, enabling battery-friendly designs. The OTP program memory allows one-time field programming suitable for prototyping, low-volume production, and legacy maintenance where code stability is paramount.
The PIC16C66 uses a Harvard RISC architecture with separate program and data buses, single-cycle instruction execution (except branches, which are two-cycle), and a deterministic interrupt structure. This makes it well suited to real-time control loops where cycle-accurate timing is required. The integrated peripherals reduce external component count, lowering BOM cost and PCB area.
Typical applications include industrial control logic, sensor interface boards, automotive body electronics (legacy subsystems), low-cost instrumentation, and embedded products requiring simple, deterministic control. The wide temperature ranges (Commercial, Industrial, Extended) also support harsh environment deployments.
When designing with this OTP MCU, note that program memory cannot be erased electrically - choose the flash-based PIC16F66 family variant (e.g., PIC16F76-I/SO) for iterative development. The 28-SOIC package has a relatively large footprint suitable for hand-soldering and through-hole-friendly prototyping.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone.
Drop-in alternatives for PIC16C66-04/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 PIC16C66-04/SO (same form factor and footprint) — differing in Package, Core, Family, Program Memory Type, Mounting Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C66-04I/SO
✅ Drop-In✓ In Stock
$5.1 / Unit
View Datasheet →PIC16C66-10/SO
✅ Drop-In✓ In Stock
$6.93 / Unit
View Datasheet →PIC16C66-20/SO
✅ Drop-In✓ In Stock
$5.45 / Unit
View Datasheet →PIC16C66-04I/SP
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16F76-I/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C66-04/SO Maximum Ratings & Electrical Characteristics
| Core | PIC16C 8-bit RISC |
| Architecture | Harvard, fully static CMOS |
| CPU Speed (max) | 4 MHz (-04 speed grade) |
| Program Memory | 14 KB OTP (8K x 14) |
| RAM | 368 bytes |
| I/O Pins | 22 |
| Package | 28-SOIC (SO) |
| Operating Voltage | 2.5 V to 6.0 V |
| Instruction Set | 35 single-word instructions |
| Timers | 3 (Timer0, Timer1, Timer2) |
| Communication | USART (SCI) |
| Peripherals | Capture/Compare/PWM (CCP), Watchdog Timer |
| Current @ 5V/4MHz | 15 µA typical |
| Current @ 3V/32kHz | 1 µA typical |
| Mounting Type | Surface Mount |
PIC16C66-04/SO Pin Configuration
| Pin 1 | MCLR/VPP — Master Clear (reset) input / programming voltage |
| Pin 2 | RA0/AN0 — PORTA bit 0 / analog input 0 |
| Pin 3 | RA1/AN1 — PORTA bit 1 / analog input 1 |
| Pin 4 | RA2/AN2 — PORTA bit 2 / analog input 2 |
| Pin 5 | RA3/AN3/VREF — PORTA bit 3 / analog input 3 / voltage reference |
| Pin 6 | RA4/T0CKI — PORTA bit 4 / Timer0 clock input (input only) |
| Pin 7 | RA5/AN4/SS — PORTA bit 5 / analog input 4 / slave select |
| Pin 8 | OSC1/CLKIN — Oscillator crystal input / external clock in |
| Pin 9 | OSC2/CLKOUT — Oscillator crystal output / clock out |
| Pin 10 | RC0/T1OSO/T1CKI — PORTC bit 0 / Timer1 oscillator output / Timer1 clock |
| Pin 11 | RC1/T1OSI/CCP2 — PORTC bit 1 / Timer1 oscillator input / CCP2 |
| Pin 12 | RC2/CCP1 — PORTC bit 2 / Capture Compare PWM 1 |
| Pin 13 | RC3/SCK/SCL — PORTC bit 3 / SPI clock / I2C clock |
| Pin 14 | RC4/SDI/SDA — PORTC bit 4 / SPI data in / I2C data |
| Pin 15 | RC5/SDO — PORTC bit 5 / SPI data out |
| Pin 16 | RC6/TX/CK — PORTC bit 6 / USART transmit / clock |
| Pin 17 | RC7/RX/DT — PORTC bit 7 / USART receive / data |
| Pin 18 | VSS — Ground reference |
| Pin 19 | VDD — Positive supply voltage |
| Pin 20 | RB0/INT — PORTB bit 0 / external interrupt |
| Pin 21 | RB1 — PORTB bit 1 |
| Pin 22 | RB2 — PORTB bit 2 |
| Pin 23 | RB3/PGM — PORTB bit 3 / low-voltage programming |
| Pin 24 | RB4 — PORTB bit 4 |
| Pin 25 | RB5 — PORTB bit 5 |
| Pin 26 | RB6/PGC — PORTB bit 6 / ICSP clock |
| Pin 27 | RB7/PGD — PORTB bit 7 / ICSP data |
| Pin 28 | VSS — Ground reference |
Typical Applications
PIC16C66-04/SO is suitable for 6 applications: Industrial Control Logic, Sensor Interface Boards, Automotive Body Electronics (Legacy), Low-Cost Instrumentation, Embedded Control Legacy Maintenance, Educational and Hobbyist Projects.
Industrial Control Logic
The PIC16C66-04/SO's 8-bit RISC architecture and 4 MHz deterministic single-cycle instruction execution make it well-suited for industrial control logic boards requiring precise timing of relay drivers, solenoid actuation, and digital I/O sequencing. With 22 I/O pins and 14 KB OTP program memory, the device can host machine state machines, ladder-logic replacements, and sensor multiplexing routines in compact 28-SOIC form factor. Low quiescent current (15 uA typical at 5V/4MHz) supports always-on industrial nodes. The OTP memory is advantageous when firmware is finalized and code security is critical. Reference design: PIC16C6X mid-range industrial control reference circuits from Microchip application notes.
Recommended
Sensor Interface Boards
The PIC16C66-04/SO's three timers (Timer0, Timer1, Timer2), capture/compare/PWM peripheral, and 8-channel 8-bit ADC make it ideal for sensor interface boards in factory automation, HVAC, and instrumentation. The 4 MHz instruction rate provides 1 MIPS throughput, adequate for sampling thermistors, pressure transducers, and digital flow sensors at typical 100 Hz to 1 kHz rates. The 368-byte RAM supports circular buffer-based averaging and moving-window filters. 22 I/O pins comfortably handle multi-sensor multiplexing. Industrial temperature variants (PIC16C66-04I/SO) extend operation to -40C to +85C for outdoor sensor enclosures.
Recommended
Automotive Body Electronics (Legacy)
The PIC16C66-04/SO has been widely deployed in legacy automotive body electronics modules - door lock controllers, window lift timers, mirror position memory, and interior lighting sequencers - where its OTP memory provides security against code reverse engineering. With 4 MHz operation, it controls relay drivers and PWM motor actuation via its CCP peripheral. Although NRND, the part remains in service for vehicle maintenance and aftermarket replacements. The 28-SOIC package enables automated assembly in high-volume automotive Tier-1 lines. For new automotive designs, the AEC-Q100-qualified PIC16F76 family is the recommended upgrade path.
Recommended
Low-Cost Instrumentation
The PIC16C66-04/SO is well-suited to low-cost digital panel meters, hand-held multimeters, and process calibrators where its 14 KB OTP memory holds calibration routines and lookup tables, while the USART enables digital communication with host PCs. The 4 MHz clock is adequate for driving LCD multiplexed displays via PORTB/PORTC bit-banging or external LCD driver ICs. The 1 MIPS throughput supports linearization math for thermocouple, RTD, and strain-gauge sensor inputs. OTP memory prevents end-user firmware tampering - important for calibration-traceable instruments. Reference design: PIC16C6X-based digital thermometer and panel meter application notes.
Recommended
Embedded Control Legacy Maintenance
The PIC16C66-04/SO is widely deployed in legacy industrial equipment, medical instruments, and military electronics where long product lifecycles (15-30 years) demand continued supply of original OTP parts. Its 28-SOIC package and standard PIC16C6X peripherals enable drop-in replacement on existing PCBs without layout changes. For maintenance contracts requiring bit-exact firmware compatibility, the original OTP part remains the only valid choice. Industrial variants extend temperature range for harsh environment service. Microchip's NRND status reflects design-tool migration rather than discontinuation of supply for legacy maintenance.
Recommended
Educational and Hobbyist Projects
The PIC16C66-04/SO's 35-instruction RISC architecture, 28-SOIC hand-solderable package, and 4 MHz simple timing make it a classic teaching platform for embedded systems courses. Students learn assembly language and C programming against the well-documented PIC16C6X family before transitioning to modern PIC16F or PIC18 devices. The OTP memory constraint forces good firmware design discipline (no iterative on-chip debug like flash parts), making it pedagogically valuable. Hobbyists replicating legacy schematics also value its continued availability through distributor stock for short-term projects. Pair with MPLAB X IDE and PICkit 3/4 for development cycle (using PIC16F76-I/SO for iterative work).
Recommended
Recommended Products Summary
Engineering reference data for PIC16C66-04/SO — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C66-04I/SO | PIC16C66-10/SO | PIC16C66-20/SO | PIC16F76-I/SO |
|---|---|---|---|---|---|
| Package | 28-SOIC | 28-SOIC - same | 28-SOIC - same | 28-SOIC - same | 28-SOIC - same |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Max Clock Frequency | 4 MHz (-04) | 4 MHz | 10 MHz | 20 MHz | 20 MHz |
| Program Memory Type | OTP (one-time) | OTP | OTP | OTP | Flash (10,000 cycles) |
| Program Memory Size | 14 KB | 14 KB | 14 KB | 14 KB | 14 KB |
| RAM | 368 bytes | 368 bytes | 368 bytes | 368 bytes | 368 bytes |
| Operating Temperature | 0C to +70C (commercial) | -40C to +85C (industrial) | 0C to +70C | 0C to +70C | -40C to +85C (industrial) |
| Lifecycle Status | NRND | NRND | NRND | NRND | Active (recommended for new designs) |
Key Differentiators
- Lower-cost commercial temperature grade variant in the same 28-SOIC footprint (vs PIC16C66-04I/SO (industrial temp grade))
- OTP memory provides inherent code security (vs PIC16F76-I/SO (flash variant))
- Slower 4 MHz speed grade for power-constrained applications (vs PIC16C66-20/SO (20 MHz speed grade))
Design Notes
Do not assume OTP memory can be re-programmed: the PIC16C66-04/SO uses One-Time-Programmable EPROM memory, which can be written only once per location. A programming error (e.g., bad fuse configuration) bricks the device permanently. For development, substitute the flash-based PIC16F76-I/SO which supports 10,000 erase/write cycles on the same 28-SOIC footprint. Reserve at least 2-3 OTP parts as engineering samples when commissioning new firmware.
Decouple VDD with a 0.1 uF ceramic capacitor placed within 5 mm of pin 20 (VDD) and pin 19/28 (VSS) for stable operation. For designs with high-current digital switching, add a bulk 10 uF tantalum or aluminum electrolytic capacitor on the supply rail. The PIC16C66-04/SO draws 15 uA typical at 5V/4MHz and 1 uA at 3V/32 kHz in sleep mode, so for battery-powered designs enable Sleep mode via the Watchdog Timer wake-up. Reference: Microchip PIC16C6X datasheet power supply decoupling section.
Estimated: the 28-SOIC package has a body length of approximately 17.9 mm and pin pitch of 1.27 mm (50 mil). For 28-SOIC hand-soldering, use a fine-tip iron (1 mm chisel) at 315 C with lead-free SAC305 solder and no-clean flux. Land pattern should be SOIC-28 with 0.65 mm pad width and 2.4 mm pad length per IPC-7351 nominal. Keep analog traces (AN0-AN4) short and away from digital switching traces to minimize ADC noise coupling on the 8-bit ADC peripheral.
Route the MCLR/VPP pin (pin 1) with a 10 kohm pull-up resistor to VDD and place a 100 nF capacitor to ground for noise immunity. The MCLR line is sensitive to voltage transients that can cause unintended resets in electrically noisy environments (motor control, relay switching). For ICSP programming access, dedicate the PGC (pin 26) and PGD (pin 27) lines to a 5-pin header. Reference Microchip development tool documentation for ICSP connection guidelines.
Compliance Information
RoHS, lead-free, and halogen-free status not explicitly stated in verified web data for PIC16C66-04/SO. The PIC16C66-04/SO is a legacy OTP part from the 1990s era before widespread lead-free conversion; check the manufacturer datasheet or contact Microchip for compliance status. Not AEC-Q100 qualified - automotive applications should use AEC-Q100-qualified parts.
