PIC16C55AT-04/SS - 8-bit OTP MCU 768B 20 I/O 4MHz SSOP-28 | Microchip
MPN: PIC16C55AT-04/SS ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.28 | $2.28 |
| 10 | $2.15 | $21.50 |
| 100 | $1.92 | $192.00 |
| 500 | $1.71 | $855.00 |
| 1,000 | $1.55 | $1,550.00 |
PIC16C55AT-04/SS Overview
What is an 8-bit OTP microcontroller? An 8-bit OTP MCU is a small, fixed-instruction-set processor whose program memory can be written exactly once (One-Time-Programmable) using an EPROM-style bit cell. The "8-bit" designation refers to the width of the ALU and the data bus; the PIC16C5X family uses a 12-bit-wide instruction word to achieve 2:1 code compression over competing 8-bit MCUs. In the broader taxonomy, OTP microcontrollers sit between mask-ROM MCUs (cheapest at high volume) and Flash MCUs (re-programmable, higher cost per bit). They are favored for cost-sensitive, high-volume, stable-firmware applications.
Key features include a RISC architecture with only 33 single-word/single-cycle instructions, an 8-bit timer/counter, a watchdog timer for reliable operation, and a power-saving SLEEP mode. The device is built on a CMOS process that yields low power consumption and high noise immunity. It supports in-circuit serial programming through Microchip's standard tools and is compatible with the PICSTART Plus and MPLAB development environments, allowing the same firmware to migrate across the PIC16C5X family.
Typical applications for the PIC16C55AT-04/SS include low-end consumer appliances, automotive sub-systems (body controllers, lighting drivers), industrial control loops, sensor interfaces, and remote-control transmitters. The 20 I/O pins are well-suited to keypad scanning, LED matrix driving, and small-stepper or DC-motor control via external drivers. The industrial-grade temperature range and SSOP footprint also enable space-constrained designs.
When designing with this device, allocate I/O pins carefully because the PIC16C5X has a fixed 12-bit program word and limited RAM (24 bytes); high-volume data structures should be stored in program memory using RETLW lookup tables. Place a 0.1 microfarad decoupling capacitor within 5 mm of VDD and use the on-chip oscillator with a 4 MHz crystal or ceramic resonator; bypass the MCLR pin according to the datasheet to ensure a clean reset.
This page synthesizes distributor pricing, drop-in alternatives from the same PIC16C5X family, and practical design notes that complement the manufacturer datasheet.
Drop-in alternatives for PIC16C55AT-04/SS — 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 PIC16C55AT-04/SS (same form factor and footprint) — differing in Package, Program Memory Size, Core Architecture, Watchdog Timer, Program Memory Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C55AT-04I/SS
✅ Drop-In✓ In Stock
$2.4 / Unit
View Datasheet →PIC16C55AT-04E/SS
✅ Drop-In✓ In Stock
$2.12 / Unit
View Datasheet →PIC16C55A-04E/P
✅ Drop-In✓ In Stock
$3.15 / Unit
View Datasheet →PIC16C554T-04/SS
✅ Drop-In✓ In Stock
$1.14 / Unit
View Datasheet →PIC16C558T-04/SS
✅ Drop-In✓ In Stock
$2.18 / Unit
View Datasheet →PIC16F54-I/SS
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C55AT-04/SS Maximum Ratings & Electrical Characteristics
| Core Architecture | PIC 8-bit RISC |
| Family | PIC16C5X |
| Program Memory Size | 768 B (512 x 12) OTP |
| Data RAM | 24 B |
| Maximum Clock Speed | 4 MHz |
| Instruction Cycle | 250 ns (4 MHz / 4) |
| Supply Voltage (VDD) | 3 V to 6.25 V |
| Number of I/O Pins | 20 |
| Timers | 1 x 8-bit |
| Watchdog Timer | Yes (on-chip) |
| Package | 28-SSOP (5.30 mm / 0.209") |
| Mounting Type | Surface Mount |
| Program Memory Type | OTP (One-Time-Programmable EPROM) |
| Operating Temperature | 0C to +70C (commercial) |
| RoHS Status | Compliant |
| Lead-Free | Yes |
PIC16C55AT-04/SS Pin Configuration
| Pin 1 | RA0 — I/O port A bit 0 |
| Pin 2 | RA1 — I/O port A bit 1 |
| Pin 3 | RA2 — I/O port A bit 2 |
| Pin 4 | RA3 — I/O port A bit 3 |
| Pin 5 | GND — Ground reference |
| Pin 6 | RB0 — I/O port B bit 0 |
| Pin 7 | RB1 — I/O port B bit 1 |
| Pin 8 | RB2 — I/O port B bit 2 |
| Pin 9 | RB3 — I/O port B bit 3 |
| Pin 10 | RB4 — I/O port B bit 4 |
| Pin 11 | RB5 — I/O port B bit 5 |
| Pin 12 | RB6 — I/O port B bit 6 |
| Pin 13 | RB7 — I/O port B bit 7 |
| Pin 14 | VDD — Positive supply voltage |
| Pin 15 | RC0 — I/O port C bit 0 |
| Pin 16 | OSC1 — Oscillator input / external clock |
| Pin 17 | OSC2 — Oscillator output (crystal mode) |
| Pin 18 | RC1 — I/O port C bit 1 |
| Pin 19 | RC2 — I/O port C bit 2 |
| Pin 20 | RC3 — I/O port C bit 3 |
| Pin 21 | RC4 — I/O port C bit 4 |
| Pin 22 | RC5 — I/O port C bit 5 |
| Pin 23 | RC6 — I/O port C bit 6 |
| Pin 24 | RC7 — I/O port C bit 7 |
| Pin 25 | NC — Not connected (per datasheet) |
| Pin 26 | NC — Not connected (per datasheet) |
| Pin 27 | NC — Not connected (per datasheet) |
| Pin 28 | MCLR — Master clear (active-low reset) |
Typical Applications
PIC16C55AT-04/SS is suitable for 6 applications: Low-End Consumer Appliance Control, Automotive Body and Lighting Modules, Industrial Sensor Interface Front-End, Remote Control and IR Transmitter, Small DC Motor and Stepper Control, Battery-Powered Wireless Sensor Tag.
Low-End Consumer Appliance Control
The PIC16C55AT-04/SS fits cost-sensitive consumer appliances (coffee makers, toasters, microwave keypads, electric toothbrush chargers) where stable firmware and the lowest per-unit BOM cost are paramount. Its 20 I/O pins drive 7-segment displays, scan 4x4 keypads, and switch relays through transistors directly. The 768-byte OTP memory holds full state machines for appliance sequencing, while 24 bytes of RAM is sufficient for timers, debounce variables and mode flags. Unlike Flash MCUs, the OTP cell reduces silicon cost and prevents unauthorized firmware read-back, an advantage in consumer markets where IP protection matters. The 5 V tolerance and 0.70 mA typical active current also suit always-on mains-powered designs without expensive regulators.
Recommended
Automotive Body and Lighting Modules
Within automotive body controllers (door locks, mirror adjusters, ambient lighting drivers, simple BCM sub-modules) the PIC16C55AT-04/SS offers 20 mA source/sink per pin capable of directly driving small LEDs and opto-isolators. The 4 MHz core handles PWM for LED dimming at audio frequencies without flicker, and the watchdog timer (WDT) recovers the module from load-dump transients on the 12 V battery rail. The E-suffix variant extends operation to -40C to +125C for under-dash or under-hood-near mounting. Where AEC-Q100 qualification is required, a Flash PIC16F-series equivalent with the same SSOP-28 footprint is preferred; the OTP part is widely used for non-safety sub-systems.
Recommended
Industrial Sensor Interface Front-End
As a sensor-interface front-end, the PIC16C55AT-04/SS reads digital sensors over GPIO bit-banging (DHT11, simple one-wire devices) and converts the data into Modbus-friendly UART frames for a downstream PLC. The 24-byte RAM is enough for a small protocol buffer plus the sensor state machine, while the 4 MHz instruction rate polls sensors at 10 Hz with margin to spare for debouncing and CRC. The watchdog timer recovers from EMI-induced lockups in factory-floor cabinets. Pin-compatible PIC16C55x variants add hardware UART for cleaner protocol handling when the firmware grows beyond what bit-banging supports in 768 OTP bytes.
Recommended
Remote Control and IR Transmitter
In handheld IR remote controls (TV, STB, AC) the PIC16C55AT-04/SS drives an IR LED through a single GPIO pin at 38 kHz carrier using timer interrupts, with the remaining I/O scanning a 5x4 keypad matrix. The 768-byte OTP holds complete code-sets for multiple protocols (RC5, NEC, SIRC) using RETLW lookup tables, and the 4 MHz oscillator supports accurate carrier generation with cycle-by-cycle control. The SLEEP mode drops active current below 1 microamp between key presses, extending battery life on coin cells. The OTP nature also prevents cloning of proprietary remote codes, an important anti-piracy feature.
Recommended
Small DC Motor and Stepper Control
Driving small brushed DC motors or unipolar stepper motors via external MOSFET/IGBT drivers, the PIC16C55AT-04/SS uses 4 I/O pins for H-bridge direction/enable and 2 pins for Hall-sensor feedback. The 8-bit timer generates PWM at 1 kHz for smooth torque, and the 4 MHz instruction rate executes a software PID loop at 200 Hz with cycle margin. The 20 mA sink capability lets the MCU directly switch the gate-driver logic inputs, removing the need for buffer ICs. Where higher step-rates are needed, the PIC16C55A-20/SS (20 MHz) executes the same algorithm five times faster, but the standard -04 part covers typical small-fan, valve, and damper actuators.
Recommended
Battery-Powered Wireless Sensor Tag
In simple wireless sensor tags that wake periodically to read a sensor and transmit a beacon, the PIC16C55AT-04/SS spends most of its life in SLEEP mode (current below 1 microamp) and wakes via watchdog timer overflow to take a reading and burst-transmit. The 24-byte RAM holds a packet frame and the 768-byte OTP stores the protocol stack and the sensor calibration table. Two GPIO pins bit-bang a UHF or sub-GHz transmitter enable/data line, while one pin powers the sensor through a MOSFET to minimize quiescent draw. Replacing the PIC16C55AT with a Flash PIC16F54-I/SS enables OTA-style firmware updates at the cost of slightly higher silicon price.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C55AT-04/SS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C55AT-04I/SS | PIC16C55AT-04E/SS | PIC16C55A-04E/P | PIC16C554T-04/SS | PIC16F54-I/SS |
|---|---|---|---|---|---|---|
| Package | 28-SSOP (5.30 mm) | 28-SSOP (5.30 mm) - same | 28-SSOP (5.30 mm) - same | 28-SSOP (5.30 mm) - same | 28-SSOP (5.30 mm) - same | 28-SSOP (5.30 mm) - same |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Program Memory | 768 B OTP (512 x 12) | 768 B OTP (512 x 12) - same | 768 B OTP (512 x 12) - same | 768 B OTP (512 x 12) - same | 768 B OTP (512 x 12) - same | 512 B Flash (256 x 12) |
| Data RAM | 24 B | 24 B - same | 24 B - same | 24 B - same | 24 B - same | 25 B (+1 B) |
| Maximum Clock | 4 MHz | 4 MHz - same | 4 MHz - same | 4 MHz - same | 4 MHz - same | 20 MHz |
| I/O Pins | 20 | 20 - same | 20 - same | 20 - same | 20 - same | 12 |
| Memory Type | OTP (One-Time-Programmable) | OTP | OTP | OTP | OTP | Flash (re-programmable) |
| Operating Temperature | 0C to +70C (commercial) | -40C to +85C (industrial) | -40C to +125C (extended) | -40C to +125C (extended) | 0C to +70C (commercial) | -40C to +85C (industrial) |
Key Differentiators
- Commercial temperature grade at the lowest OTP BOM cost (vs PIC16C55AT-04I/SS)
- Wide 3 V to 6.25 V supply range supports both 3.3 V and 5 V rails (vs PIC16F54-I/SS)
- 768-byte OTP holds 33% more code than the older PIC16C54A (vs PIC16C54A-04/SS)
- 20 mA source/sink on every GPIO removes external drivers for low-current loads (vs PIC16C554T-04/SS)
Design Notes
Place a 0.1 microfarad decoupling capacitor (X7R ceramic) within 5 mm of the VDD pin (pin 14) and a bulk 1 to 10 microfarad electrolytic at the board's supply input. The PIC16C55AT-04/SS draws roughly 0.7 mA active at 4 MHz and below 1 microamp in SLEEP, so the supply rail can be shared with low-power analog circuitry if decoupled locally. The MCLR pin (pin 28) requires a 10 kohm pull-up to VDD and a 100 nF capacitor to ground if the internal reset is not used; otherwise a clean reset is not guaranteed.
Use a 28-SSOP land pattern per IPC-7351 (0.65 mm pitch, 5.30 mm body width) with NSMD pads for reliable solder joint inspection. Keep the 4 MHz crystal or resonator within 5 mm of OSC1 (pin 16) and OSC2 (pin 17) with a ground guard ring on the PCB layer beneath to reduce EMI coupling into adjacent traces. Route MCLR and VDD traces first and avoid running long parallel tracks under the oscillator to minimise cross-talk and reset glitches.
Do not rely on the OTP device for prototype firmware iteration; the cell can be written only once, so a code bug requires a new part. Migrate development to the pin-compatible PIC16F54-I/SS Flash variant, then transfer the validated hex to the PIC16C55AT-04/SS for production. Also note that the PIC16C5X core has only one 8-bit file register for arithmetic; larger math operations need careful carry management, and the PCLATH register must be set correctly before computed GOTOs or table reads.
The PIC16C55AT-04/SS GPIO pins sink up to 20 mA but the combined source current is limited to 150 mA across the whole package; if you drive many LEDs simultaneously, use a low-side MOSFET array and PWM the gates instead of driving each LED from a GPIO. This keeps the die within its thermal envelope and prevents logic-level degradation on neighbouring pins due to internal bond-wire resistance.
Compliance Information
RoHS and lead-free confirmed by Microchip product page. AEC-Q100 not qualified at the PIC16C55AT-04/SS grade; choose the E-suffix extended-temperature variant for automotive enclosures.
