PIC16C55A-04I/SS - 4MHz 8-bit OTP MCU, 20 I/O, SSOP-28 | Microchip
MPN: PIC16C55A-04I/SS β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.45 | $3.45 |
| 10 | $3.1 | $31.00 |
| 100 | $2.78 | $278.00 |
| 500 | $2.5 | $1,250.00 |
| 1,000 | $2.22 | $2,220.00 |
PIC16C55A-04I/SS Overview
What is a microcontroller? A microcontroller (MCU) is a single-chip computer containing a CPU, non-volatile program memory, working RAM, configurable I/O peripherals, and one or more timers on one piece of silicon. Within the broader taxonomy, an MCU is a sub-category of integrated circuit -> microprocessor -> semiconductor. The PIC16C5X family is positioned as an entry-level 8-bit RISC MCU optimized for cost-sensitive, low-pin-count embedded control, where its compact 33-instruction instruction set and 12-bit-wide opcode enable 2:1 code compression versus typical 8-bit CISC competitors in the same price class.
Key features of the PIC16C55A include only 33 single-word/single-cycle instructions (most execute in 200 ns at 20 MHz oscillator, equivalent to a 4 MHz instruction rate for the -04 speed grade), a 2-level hardware call stack, direct/indirect/relative addressing modes for both data and instructions, and seven or eight special-function hardware registers. An 8-bit real-time clock/counter (TMR0) with user-programmable prescaler supports timing, event-counting, and pulse-width measurement. The on-chip watchdog timer (WDT) with its own on-chip RC oscillator enables autonomous recovery from code-flow faults without external components, which is critical for unattended industrial installations. Power-saving SLEEP mode reduces I_DD to a few microamps for battery-operated applications, and the device operates across 2.5 V to 6.25 V V_DD.
Architecturally, the PIC16C55A employs a Harvard-style RISC core with separate program and data paths, providing deterministic instruction throughput and immunity to data-bus contention. The OTP EPROM is windowless and one-time-programmable, giving the device its 'C' (CMOS/OTP) designation; for windowed UV-erasable prototypes, the JW ceramic package variant exists. The 12-bit instruction word delivers strong code density, and the all-static design permits the oscillator to be stopped without losing internal register state - a useful trait for low-power designs.
Typical applications include appliance controls, automotive body electronics, low-end security panels, simple sensor signal conditioning, fan and pump controllers, and any high-volume embedded product where cost, small footprint, and proven PIC ecosystem tooling outweigh the need for modern peripherals like USB or CAN. Because the part is marked 'Not Recommended for new designs' by Microchip, it is best reserved for maintenance of installed equipment.
When designing with the PIC16C55A, note that the 4 MHz speed grade limits computational throughput; verify instruction-cycle margins at your maximum external event rate. Decoupling V_DD with a 0.1 uF ceramic capacitor placed within 5 mm of the supply pin, plus a 10 uF bulk reservoir at the regulator output, is essential for clean POR behavior on industrial supply rails.
This page consolidates current distributor pricing, parametric drop-in alternatives, and engineering design notes not typically aggregated on a single datasheet - giving maintenance and sourcing engineers a one-stop reference for legacy PIC16C55A inventory decisions.
Drop-in alternatives for PIC16C55A-04I/SS β 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 PIC16C55A-04I/SS (same form factor and footprint) β differing in Package, Program Memory Size, Core Architecture, Timers, Instruction Set.
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Request AlternativesPIC16C55A-04I/SS Maximum Ratings & Electrical Characteristics
| Family | PIC16C5X |
| Core | 8-bit RISC |
| Program Memory Type | OTP EPROM |
| Program Memory Size | 768 bytes (512 x 12) |
| RAM Size | 24 bytes |
| Maximum Clock Frequency | 4 MHz |
| Instruction Set | 33 single-word/single-cycle instructions |
| I/O Pins | 20 |
| Timers | 1 x 8-bit (TMR0) |
| Hardware Stack Depth | 2 levels |
| Watchdog Timer | Yes, with on-chip RC oscillator |
| Operating Voltage (V_DD) | 2.5 V to 6.25 V |
| Operating Temperature | -40C to +85C (Industrial) |
| Package | SSOP-28 |
| Mounting Type | Surface Mount |
| Speed Grade | 04 (4 MHz) |
| Lifecycle Status | Not Recommended for new designs (NRND) |
PIC16C55A-04I/SS Pin Configuration
| Pin 1 | RA0 β Bidirectional I/O, PORTA bit 0 |
| Pin 2 | RA1 β Bidirectional I/O, PORTA bit 1 |
| Pin 3 | RA2 β Bidirectional I/O, PORTA bit 2 |
| Pin 4 | RA3 β Bidirectional I/O, PORTA bit 3 |
| Pin 5 | /MCLR β Master Clear reset input (active-low) |
| Pin 6 | OSC1 β Oscillator input / external clock input |
| Pin 7 | OSC2 β Oscillator output (crystal mode) |
| Pin 8 | V_DD β Positive supply voltage |
| Pin 9 | RB0 β Bidirectional I/O, PORTB bit 0 |
| Pin 10 | RB1 β Bidirectional I/O, PORTB bit 1 |
| Pin 11 | RB2 β Bidirectional I/O, PORTB bit 2 |
| Pin 12 | RB3 β Bidirectional I/O, PORTB bit 3 |
| Pin 13 | RB4 β Bidirectional I/O, PORTB bit 4 |
| Pin 14 | RB5 β Bidirectional I/O, PORTB bit 5 |
| Pin 15 | RB6 β Bidirectional I/O, PORTB bit 6 |
| Pin 16 | RB7 β Bidirectional I/O, PORTB bit 7 |
| Pin 17 | RC0 β Bidirectional I/O, PORTC bit 0 (PIC16C55A) |
| Pin 18 | RC1 β Bidirectional I/O, PORTC bit 1 |
| Pin 19 | RC2 β Bidirectional I/O, PORTC bit 2 |
| Pin 20 | RC3 β Bidirectional I/O, PORTC bit 3 |
| Pin 21 | RC4 β Bidirectional I/O, PORTC bit 4 |
| Pin 22 | RC5 β Bidirectional I/O, PORTC bit 5 |
| Pin 23 | RC6 β Bidirectional I/O, PORTC bit 6 |
| Pin 24 | RC7 β Bidirectional I/O, PORTC bit 7 |
| Pin 25 | T0CKI β Timer0 clock input (shared function on RC pin) |
| Pin 26 | V_SS β Ground reference |
| Pin 27 | V_DD β Positive supply (second bond) |
| Pin 28 | NC β Not connected (per datasheet pinout) |
Typical Applications
PIC16C55A-04I/SS is suitable for 6 applications: Appliance Control Boards, Low-End Security Panels, Automotive Body Electronics, Fan and Pump Speed Controllers, Industrial Sensor Signal Conditioning, Legacy Maintenance and Spare-Part Stocking.
Appliance Control Boards
The PIC16C55A-04I/SS is a strong fit for appliance control boards because its 4 MHz clock and 8-bit RISC core deliver enough throughput for motor timing, sensor polling, and relay sequencing at very low unit cost. With 20 I/O pins it can directly drive TRIAC control lines, read temperature sensors through analog comparators or PWM, and toggle indicator LEDs without external mux logic. The on-chip watchdog timer autonomously recovers from supply glitches on noisy appliance power rails. Programming is via 33 single-cycle instructions that any PIC engineer can master in days, keeping firmware development cost low.
Recommended
Low-End Security Panels
For low-end security keypad panels and PIR-sensor interface boards, the PIC16C55A-04I/SS provides the right balance of cost and capability: 24 bytes RAM is sufficient for keypad debounce state, 768 bytes EPROM fits sensor-scan algorithms, and 20 I/O lines connect to key-matrix rows, piezo buzzers, status LEDs, and relay outputs. Industrial temperature rating supports indoor equipment near exterior walls where temperatures swing. Watchdog timer prevents permanent lockup if the panel bus is glitched. OTP EPROM protects firmware IP from casual cloning.
Recommended
Automotive Body Electronics
Within automotive body electronics - door modules, mirror controllers, simple lighting drivers - the PIC16C55A-04I/SS handles relay sequencing and switch-matrix reading at sub-$3 cost. Its 2.5 V to 6.25 V supply range tolerates load-dump transients when paired with external TVS diodes. Note that AEC-Q100 qualification is not specified, so for safety-critical systems an automotive-qualified alternative like PIC16F1823-I/SL should be selected. Industrial temperature grade (-40C to +85C) covers most underhood-adjacent locations and cabin environments.
Recommended
Fan and Pump Speed Controllers
Closed-loop fan and pump speed controllers benefit from the PIC16C55A-04I/SS's 8-bit TMR0 timer with prescaler, which directly measures tachometer pulses from a Hall sensor or back-EMF zero-cross detection. PWM output on a single I/O pin drives a logic-level MOSFET or optocoupler/TRIAC pair for AC line applications. The 4 MHz instruction rate supports 1 ms control-loop periods with comfortable headroom for 20-point PID calculations. OTP EPROM locks in calibrated PWM tables that match motor characteristics at production time.
Recommended
Industrial Sensor Signal Conditioning
Sensor interface boards for limit switches, photoelectric eyes, and simple 4-20 mA loops often pair a PIC16C55A-04I/SS with an external ADC and analog front end. The MCU handles threshold logic, debounce, and Modbus-free serial communication over a UART-emulated bit-banged port. Twenty I/O lines allow direct multiplexing for multi-channel sensor panels. Industrial temperature grade and 2.5 V to 6.25 V supply tolerance suit 24V industrial control cabinets with proper regulation. Watchdog timer ensures recovery from supply brownouts common in factory environments.
Recommended
Legacy Maintenance and Spare-Part Stocking
Because Microchip marks PIC16C55A-04I/SS as 'Not Recommended for new designs', its most appropriate application today is maintaining installed equipment: industrial controllers, appliance boards, and security panels already in the field that need field-replacement spares. The industrial temperature grade matches the operating environment of most installed systems. Sourcing engineers should stockpile last-time-buy quantities and evaluate PIC16F54-I/SS as the Flash-programmable modern equivalent for any board being redesigned. This prevents unplanned downtime when factory support ends.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C55A-04I/SS β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C55A-04/SS | PIC16C55A-04E/SS | PIC16C55-10I/SS | PIC16C55A-04I/SP | PIC16C55A-04I/SO |
|---|---|---|---|---|---|---|
| Package | SSOP-28 | SSOP-28 - same | SSOP-28 - same | SSOP-28 - same | SPDIP-28 - through-hole | SOIC-28 - wide-body |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Maximum Clock Frequency | 4 MHz | 4 MHz | 4 MHz | 10 MHz (+150%) | 4 MHz | 4 MHz |
| Operating Temperature | -40C to +85C (Industrial) | 0C to +70C (Commercial) | -40C to +125C (Extended) | -40C to +85C (Industrial) | -40C to +85C (Industrial) | -40C to +85C (Industrial) |
| Program Memory Type | OTP EPROM | OTP EPROM | OTP EPROM | OTP EPROM | OTP EPROM | OTP EPROM |
| Program Memory Size | 768 bytes (512 x 12) | 768 bytes (512 x 12) | 768 bytes (512 x 12) | 768 bytes (512 x 12) | 768 bytes (512 x 12) | 768 bytes (512 x 12) |
| I/O Pins | 20 | 20 | 20 | 20 | 20 | 20 |
| Operating Voltage | 2.5 V to 6.25 V | 2.5 V to 6.25 V | 2.5 V to 6.25 V | 2.5 V to 6.25 V | 2.5 V to 6.25 V | 2.5 V to 6.25 V |
| Lifecycle Status | NRND | NRND | NRND | NRND | NRND | NRND |
Key Differentiators
- Industrial temperature grade in a compact SSOP-28 package (vs PIC16C55A-04/SS)
- Extended temperature range for high-ambient installations (vs PIC16C55A-04I/SS)
- Doubled instruction throughput for tighter control loops (vs PIC16C55-10I/SS)
Design Notes
Place a 0.1 uF ceramic decoupling capacitor within 5 mm of the V_DD pin (pin 8 on SSOP-28) and a 10 uF bulk reservoir at the regulator output. The PIC16C5X family is sensitive to V_DD ripple during POR; inadequate decoupling can cause intermittent code execution at startup on industrial supplies. If the board draws high current from switching relays, add a ferrite bead in series with V_DD.
Do not leave /MCLR floating - tie it through a 10 kohm pull-up to V_DD. A floating /MCLR pin picks up noise on long PCB traces and randomly resets the MCU in electrically noisy environments. For in-circuit serial programming (ICSP) headers, add the standard 10 kΞ© pull-up plus a diode to V_DD as documented in Microchip programming specifications.
Keep the oscillator traces (OSC1 pin 6, OSC2 pin 7) short and surrounded by a ground pour to minimize EMI radiation and susceptibility. For a four-pin crystal resonator, place the load capacitors (typically 15-33 pF) within 2 mm of the oscillator pins. In noisy switching applications consider a 4-pin ceramic resonator over a discrete crystal to reduce BOM and improve start-up under vibration.
The PIC16C55A-04I/SS in SSOP-28 has a typical thermal resistance of approximately 90 C/W junction-to-ambient. At full operating speed and worst-case industrial temperature (85C ambient), junction rise stays under 10 C, so no heatsink is required. However, when outputs source or sink high current (20 mA per pin x 20 mA total subject to package dissipation), calculate dissipation as P = I x V_DD and verify against the absolute maximum junction temperature of 150 C.
Compliance Information
RoHS/REACH compliance per Microchip product page. AEC-Q100 not qualified - for automotive safety-critical applications use AEC-Q100 qualified alternatives such as PIC16F1823-I/SL. Lead-free and halogen-free per Microchip material declarations.
