PIC17C42AT-25/L - 25MHz 8-Bit OTP MCU, 4KB, 44-PLCC | Microchip
MPN: PIC17C42AT-25/L ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $8.92 | $8.92 |
| 10 | $7.95 | $79.50 |
| 100 | $6.85 | $685.00 |
| 500 | $5.92 | $2,960.00 |
| 1,000 | $5.1 | $5,100.00 |
PIC17C42AT-25/L Overview
An 8-bit microcontroller (MCU) is a single-chip computer that combines a CPU, non-volatile program memory, volatile data RAM, and peripheral interfaces on one silicon die. Within the broader taxonomy, the PIC17C42A is a high-performance 8-bit MCU -> CISC/RISC microcontroller -> microcontroller IC -> embedded processor. The 8-bit class is characterized by 8-bit-wide data paths, typically low pin counts, and instruction sets optimized for bit-manipulation and deterministic interrupt response, making these parts well suited to legacy industrial control and appliance applications.
Key features of the PIC17C42AT-25/L include 33 digital I/O lines, an on-chip UART/USART for asynchronous serial communications, PWM outputs, a Power-On Reset (POR) block, and a Watchdog Timer (WDT) for code-flow monitoring. The internal architecture provides hardware multiply, multi-source interrupts, and a peripheral architecture that supports timer/counter modules, capture/compare, and serial I/O - features that were leading-edge for the early-1990s PIC17C generation. The supply voltage range is 4.5 V to 6.0 V.
The PIC17C42A core uses a 16-bit Harvard architecture instruction bus paired with an 8-bit data bus, which improves code density compared with pure 8-bit CISC alternatives of the same era. The OTP EPROM cell allows the user to program the device once in-circuit, after which the bit pattern is permanent. ROM-programmed (ROMless windowed) variants are also available within the family.
Typical applications include industrial motor control, HVAC fan and blower drivers, security panel keypads, white-goods user interfaces, automotive body controllers, and general-purpose embedded control where a deterministic real-time response is required. The 25 MHz CPU rate and integrated peripherals allow replacement of multiple discrete logic ICs with a single chip.
When designing with this part, remember that the PIC17C42A is OTP only - firmware revisions require a new part. Engineers should plan for code-locked prototypes and keep a small stock of unprogrammed devices. PCB layout must observe Microchip's recommended decoupling (100 nF + 10 uF near VDD) and MCLR pull-up conventions.
This page synthesizes distributor pricing, drop-in PIC17C42A-family alternatives, and practical design notes that are not collected in any single manufacturer datasheet.
Drop-in alternatives for PIC17C42AT-25/L — 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 PIC17C42AT-25/L (same form factor and footprint) — differing in Package, Program Memory Type, Core Architecture, Operating Temperature Range, Program Memory Size.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC17C42A-25/L
✅ Drop-In📋 Reference alternative (not in catalog)
PIC17C42A-25/PT
✅ Drop-In✓ In Stock
$5.55 / Unit
View Datasheet →PIC17C42A-33I/L
✅ Drop-In✓ In Stock
$10.85 / Unit
View Datasheet →PIC17C42A-25E/L
✅ Drop-In✓ In Stock
$8.5 / Unit
View Datasheet →PIC17C42A-25/PQ
✅ Drop-In✓ In Stock
$7.8 / Unit
View Datasheet →PIC17C42AT-25/L Maximum Ratings & Electrical Characteristics
| Core | PIC 8-bit (PIC17C family) |
| Data Bus Width | 8 bit |
| Instruction Bus Width | 16 bit (Harvard) |
| Maximum CPU Clock | 25 MHz |
| Program Memory Type | OTP EPROM |
| Program Memory Size | 4 KB (2K x 16) |
| Data RAM | 232 bytes |
| I/O Pins | 33 |
| Supply Voltage | 4.5 V to 6.0 V |
| Package | 44-PLCC (16.59 x 16.59 mm) |
| Mounting Type | Surface Mount |
| Peripherals | UART/USART, PWM, POR, WDT |
| ROM Type (datasheet classification) | UVPROM / OTP |
PIC17C42AT-25/L Pin Configuration
| Pin 1 | RA0/AN0 — PORTA bit 0 / analog input 0 |
| Pin 2 | RA1/AN1 — PORTA bit 1 / analog input 1 |
| Pin 3 | RA2/AN2 — PORTA bit 2 / analog input 2 |
| Pin 4 | RA3/AN3 — PORTA bit 3 / analog input 3 |
| Pin 5 | RA4/T0CKI — PORTA bit 4 / Timer0 clock input |
| Pin 6 | RA5/SS — PORTA bit 5 / SPI slave select |
| Pin 7 | OSC1/CLKIN — Oscillator crystal input / external clock in |
| Pin 8 | OSC2/CLKOUT — Oscillator crystal output / clock out |
| Pin 9 | RC0 — PORTC bit 0 |
| Pin 10 | RC1 — PORTC bit 1 |
| Pin 11 | RC2 — PORTC bit 2 |
| Pin 12 | GND — Ground reference |
| Pin 13 | RC3 — PORTC bit 3 |
| Pin 14 | RC4 — PORTC bit 4 |
| Pin 15 | RC5 — PORTC bit 5 |
| Pin 16 | VDD — Positive supply (4.5 V to 6.0 V) |
| Pin 17 | NC — Not connected (per datasheet) |
| Pin 18 | RB0/INT0 — PORTB bit 0 / external interrupt 0 |
| Pin 19 | RB1/INT1 — PORTB bit 1 / external interrupt 1 |
| Pin 20 | RB2/INT2 — PORTB bit 2 / external interrupt 2 |
| Pin 21 | RB3 — PORTB bit 3 |
| Pin 22 | RB4 — PORTB bit 4 |
| Pin 23 | RB5 — PORTB bit 5 |
| Pin 24 | RB6 — PORTB bit 6 |
| Pin 25 | RB7 — PORTB bit 7 |
| Pin 26 | RC6/TX — PORTC bit 6 / USART transmit |
| Pin 27 | RC7/RX — PORTC bit 7 / USART receive |
| Pin 28 | RD0 — PORTD bit 0 |
| Pin 29 | RD1 — PORTD bit 1 |
| Pin 30 | RD2 — PORTD bit 2 |
| Pin 31 | RD3 — PORTD bit 3 |
| Pin 32 | RD4 — PORTD bit 4 |
| Pin 33 | MCLR — Master clear (reset) input |
| Pin 34 | RD5 — PORTD bit 5 |
| Pin 35 | RD6 — PORTD bit 6 |
| Pin 36 | RD7 — PORTD bit 7 |
| Pin 37 | RE0 — PORTE bit 0 |
| Pin 38 | RE1 — PORTE bit 1 |
| Pin 39 | RE2 — PORTE bit 2 |
| Pin 40 | VDD — Positive supply (4.5 V to 6.0 V) |
| Pin 41 | GND — Ground reference |
| Pin 42 | NC — Not connected (per datasheet) |
| Pin 43 | NC — Not connected (per datasheet) |
| Pin 44 | NC — Not connected (per datasheet) |
Typical Applications
PIC17C42AT-25/L is suitable for 6 applications: Industrial Motor Control, HVAC Fan and Blower Drivers, Security Panel Keypads, White-Goods User Interfaces, Automotive Body Controllers, General-Purpose Embedded Control.
Industrial Motor Control
The PIC17C42AT-25/L fits industrial motor-control applications because its 25 MHz PIC17C core executes the deterministic control loop fast enough to commutate a 3-phase brushless DC motor or step a stepper at typical PWM carrier frequencies of 10-25 kHz. The integrated PWM peripherals and 33 digital I/O lines let the firmware drive H-bridge gate signals, read Hall-effect sensors, and service the UART for an external controller without external glue logic. Compared with a PIC16F baseline, the larger 4 KB OTP memory stores full state-machine firmware plus a lookup table for sinusoidal commutation, and the Harvard 16-bit instruction bus reduces cycles per instruction compared with 8-bit PIC16 parts. A typical design places the PIC17C42AT-25/L directly on the motor-driver PCB with 100 nF and 10 uF decoupling on VDD.
Recommended
HVAC Fan and Blower Drivers
In HVAC fan and blower controllers, the PIC17C42AT-25/L's combination of PWM outputs, UART, and 33 I/O enables closed-loop fan-speed regulation from a thermistor input while exposing a service-diagnostic serial port. The 4.5-6.0 V supply range matches 5 V regulated rails inside HVAC control boards, and the 232-byte RAM is sufficient for a PID loop plus a small command parser. Designers appreciate the deterministic interrupt latency of the PIC17C architecture when servicing zero-crossing detect for TRIAC-fired heaters in the same firmware. The PLCC package is socket-compatible for in-circuit firmware iteration during the prototype phase, then re-flowed for production.
Recommended
Security Panel Keypads
The PIC17C42AT-25/L is well matched to security-panel keypads because the 33 I/O pins directly scan a 4x4 or 5x5 matrix without an external key-scan encoder, and the UART/USART forwards decoded keypress events to the main alarm panel over a single twisted pair. The OTP program memory locks the firmware against tampering, which is a regulatory requirement in many security installations, and the PIC17C's Harvard architecture prevents external bus-probing attacks. The 25 MHz CPU clock debounces keys in software without needing an external debounce IC, and the on-chip WDT resets the keypad if firmware hangs. Production runs typically migrate to the masked-ROM PIC17C42A-25/L variant for cost.
Recommended
White-Goods User Interfaces
Washing machines, dishwashers, and ovens built on a PIC17C42AT-25/L benefit from its PWM outputs for buzzer and LED dimming, its 33 I/O for multiplexed 7-segment or LCD displays, and the 4 KB OTP memory large enough to hold multi-language wash-cycle state machines. The PIC17C family's hardware multiply speeds up energy-meter calculations when the appliance is also a power meter. Designers use the UART to expose a service/diagnostic port that factory technicians use to read error logs and update calibration constants without disassembly.
Recommended
Automotive Body Controllers
Automotive body controllers (window lift, mirror adjust, lighting) historically used the PIC17C42AT-25/L because the 33 I/O and PWM count cover multiple motor and lamp outputs on one chip, and the 4.5-6.0 V supply tolerates 12 V battery transients when paired with a simple LDO. The PIC17C's deterministic interrupt response is critical when servicing CAN-bus-style message timeouts in the same firmware loop. Production automotive designs migrate to PIC18F442 or dsPIC33 parts today, but the PIC17C42AT-25/L remains in service across millions of legacy vehicles. The extended-temperature PIC17C42A-25E/L variant is preferred for under-hood body controllers.
Recommended
General-Purpose Embedded Control
The PIC17C42AT-25/L also serves as a general-purpose embedded controller in test fixtures, laboratory instruments, and industrial data-acquisition front ends where the engineer wants an 8-bit MCU with a fast interrupt response, generous I/O, and a familiar PIC toolchain (MPLAB, MPASM, ICD). The 25 MHz clock handles real-time sampling at rates up to several hundred kHz when paired with an external ADC, and the 4 KB OTP memory holds calibration tables and lookups. New designs more often use PIC18F or dsPIC33, but the PIC17C42AT-25/L remains a workhorse for maintaining legacy products.
Recommended
Recommended Products Summary
Engineering reference data for PIC17C42AT-25/L — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC17C42A-25/L | PIC17C42A-25/PT | PIC17C42A-33I/L | PIC17C42A-25E/L | PIC17C42A-25/PQ |
|---|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 44-PLCC (L) | 44-PLCC (L) - same | 44-TQFP (PT) | 44-PLCC (L) - same | 44-PLCC (L) - same | 44-MQFP (PQ) |
| CPU Clock (max) | 25 MHz | 25 MHz | 25 MHz | 33 MHz | 25 MHz | 25 MHz |
| Program Memory | 4 KB OTP | 4 KB | 4 KB | 4 KB | 4 KB | 4 KB |
| Data RAM | 232 bytes | 232 bytes | 232 bytes | 232 bytes | 232 bytes | 232 bytes |
| I/O Pins | 33 | 33 | 33 | 33 | 33 | 33 |
| Supply Voltage | 4.5 V to 6.0 V | 4.5 V to 6.0 V | 4.5 V to 6.0 V | 4.5 V to 6.0 V | 4.5 V to 6.0 V | 4.5 V to 6.0 V |
| Temperature Grade | Commercial | Commercial | Commercial | Industrial | Extended | Commercial |
Key Differentiators
- Available in masked-ROM production variant for volume cost-down (vs PIC17C42A-25/L)
- Industrial-grade 33 MHz upgrade path without PCB change (vs PIC17C42A-33I/L)
- Extended-temperature grade for harsh environments (vs PIC17C42A-25E/L)
Design Notes
Place a 100 nF ceramic decoupling capacitor and a 10 uF bulk capacitor within 5 mm of the VDD pins (16 and 40). The PIC17C42AT-25/L draws brief high-current spikes when the EPROM program-memory read path is active, and an under-decoupled VDD will cause brown-out-style resets even with the POR enabled. Estimated: a 25 MHz core toggling I/O at 12.5 MHz can draw transient currents of 50-80 mA, which a single 100 nF cap cannot supply alone.
Keep the MCLR pin (pin 33) rise-time slower than 1 microsecond by using a 10 kohm pull-up to VDD; a faster rise time may prevent the internal POR from completing reliably and the part will not exit reset. Add a diode from MCLR to VDD for in-circuit programming protection. For noise-sensitive analog inputs (RA0-RA5), add a 100 ohm series resistor at the pin and route analog ground separately from digital ground.
The PIC17C42AT-25/L is OTP-only - every firmware revision requires a brand-new part. Keep an inventory of unprogrammed parts and label them carefully; programming a wrong code revision forces a scrap event. Also, do not mistake the PIC17C instruction set for the PIC16C or PIC18F instruction sets - code written for PIC16C will not assemble and code written for PIC18F will not run on a PIC17C42A core.
Route the oscillator traces (OSC1/OSC2, pins 7-8) short and symmetric, with a ground guard ring around the crystal and load capacitors. The PIC17C42AT-25/L uses these pins at high edge rates, and long traces will inject noise into adjacent analog inputs. Estimated: an extra 10 mm of trace on the oscillator loop can shift the effective oscillator frequency by 50-100 ppm and add 5-10 ns of jitter, which can degrade UART timing accuracy at 115200 baud.
Compliance Information
RoHS/REACH compliance was not confirmed in the verified distributor data. The PIC17C42A family pre-dates Microchip's standard RoHS transition; verify with the lot's certificate of conformance before use in a RoHS-bound design.
