PIC16C55-XTI/SO - 8-bit 4MHz 768B OTP MCU, 28-SOIC | Microchip
MPN: PIC16C55-XTI/SO ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $4.5 | $4.50 |
| 10 | $4.05 | $40.50 |
| 100 | $3.6 | $360.00 |
| 500 | $3.2 | $1,600.00 |
| 1,000 | $2.85 | $2,850.00 |
PIC16C55-XTI/SO Overview
A microcontroller (MCU) is a single-chip computer that contains a CPU, memory, and peripherals. It belongs to the hierarchy MCU -> microcontroller -> embedded controller -> semiconductor device. The PIC16C5X family pioneered low-cost, high-performance 8-bit RISC control and remains popular for low-cost, deterministic embedded tasks where 8-bit simplicity is sufficient.
Key features include a 4 MHz maximum clock rate, two-level deep hardware stack, direct/indirect/relative addressing modes, an 8-bit real-time clock/counter (TMR0), and seven or eight special-function hardware registers. Seven special-function hardware registers on this part optimize instruction decoding and context save/restore for interrupt-free operation.
The PIC16C55-XTI/SO uses a Harvard architecture with separate program and data buses, fully static CMOS design allowing clock operation down to DC, and 12-bit wide instructions with 2:1 code compression over typical 8-bit CISC microcontrollers. RISC architecture with 33 single-cycle instructions (PIC16C5X baseline) delivers predictable timing with most instructions executing in one instruction cycle (4 clock periods). The "XT" speed grade designates operation with a standard crystal or resonator oscillator, and "I" designates the industrial -40C to +85C operating range.
Typical applications include simple embedded control tasks, low-cost consumer appliances, industrial sensor interfaces, and legacy designs requiring OTP-programmed 8-bit RISC controllers. The 28-pin SOIC wide-body footprint suits through-hole-replacement PCB retrofit projects where a standard 0.3-inch-wide SOIC is acceptable.
When designing with this part, ensure your oscillator selection matches the "XT" grade (typically a 4 MHz crystal with two 22-33 pF load capacitors). Use MPLAB PM3 or equivalent device programmer to program the OTP memory only once - if field re-programmability is needed, consider the PIC16F55 Flash variant. The 24-byte RAM limits data buffering, so use of small state machines and polling rather than large stacks is recommended.
This page synthesizes distributor pricing, pin-compatible OTP PIC16C5X alternatives, and practical 8-bit design notes not found on the standalone manufacturer datasheet.
Drop-in alternatives for PIC16C55-XTI/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 PIC16C55-XTI/SO (same form factor and footprint) — differing in Program Memory Size, Program Memory Type, Mounting Type, RAM Size, Maximum Clock Frequency.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C55T-XTI/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C55T-RCI/SO
✅ Drop-In✓ In Stock
$5.45 / Unit
View Datasheet →PIC16C55T-LPI/SO
✅ Drop-In✓ In Stock
$2.49 / Unit
View Datasheet →PIC16C55T-HSI/SO
✅ Drop-In✓ In Stock
$5.2 / Unit
View Datasheet →PIC16C55T-HSE/SO
✅ Drop-In✓ In Stock
$5.74 / Unit
View Datasheet →PIC16C55-RCI/SO
✅ Drop-In✓ In Stock
$1.85 / Unit
View Datasheet →PIC16C55-XTI/SO Maximum Ratings & Electrical Characteristics
| Series | PIC® 16C |
| Core Processor | PIC |
| Core Size | 8-bit |
| Maximum Clock Frequency | 4 MHz |
| Program Memory Size | 768 B (512 x 12) |
| Program Memory Type | OTP (One-Time Programmable) |
| RAM Size | 24 B |
| Number of I/O Pins | 20 |
| Supply Voltage Range | 3.3 V / 5 V (3.0 V - 6.0 V operating) |
| Operating Temperature Range | -40C to +85C (Industrial) |
| Package / Case | 28-SOIC (0.295 inch wide body) |
| Mounting Type | Surface Mount |
| Oscillator Type | XT (crystal/resonator) |
| Data Converters | None (no on-chip ADC) |
| Connectivity | None (no UART/SPI/I2C on this base part) |
| Peripherals | TMR0 (8-bit timer/counter), WDT |
| ROM Type | EPROM/OTP |
| Instruction Set Width | 12-bit |
| Hardware Stack Depth | 2 levels |
| MSL Level | 1 (unlimited floor life) |
PIC16C55-XTI/SO Pin Configuration
| Pin 1 | RA0 — Bidirectional I/O port A bit 0 |
| Pin 2 | RA1 — Bidirectional I/O port A bit 1 |
| Pin 3 | RA2 — Bidirectional I/O port A bit 2 |
| Pin 4 | RA3 — Bidirectional I/O port A bit 3 |
| Pin 5 | RB0 — Bidirectional I/O port B bit 0 |
| Pin 6 | RB1 — Bidirectional I/O port B bit 1 |
| Pin 7 | RB2 — Bidirectional I/O port B bit 2 |
| Pin 8 | RB3 — Bidirectional I/O port B bit 3 |
| Pin 9 | RB4 — Bidirectional I/O port B bit 4 |
| Pin 10 | RB5 — Bidirectional I/O port B bit 5 |
| Pin 11 | RB6 — Bidirectional I/O port B bit 6 |
| Pin 12 | RB7 — Bidirectional I/O port B bit 7 |
| Pin 13 | RC0 — Bidirectional I/O port C bit 0 |
| Pin 14 | RC1 — Bidirectional I/O port C bit 1 |
| Pin 15 | RC2 — Bidirectional I/O port C bit 2 |
| Pin 16 | OSC1 — Oscillator crystal input (XT mode) |
| Pin 17 | OSC2 — Oscillator crystal output (XT mode) |
| Pin 18 | RC3 — Bidirectional I/O port C bit 3 |
| Pin 19 | RC4 — Bidirectional I/O port C bit 4 |
| Pin 20 | RC5 — Bidirectional I/O port C bit 5 |
| Pin 21 | RC6 — Bidirectional I/O port C bit 6 |
| Pin 22 | RC7 — Bidirectional I/O port C bit 7 |
| Pin 23 | VSS — Ground reference |
| Pin 24 | VDD — Positive supply voltage (3.0 - 6.0 V) |
| Pin 25 | T0CKI — Timer0 clock input / RA4 |
| Pin 26 | MCLR — Master clear reset input (active low) |
| Pin 27 | RA5 — Bidirectional I/O port A bit 5 |
| Pin 28 | RA6 — Bidirectional I/O port A bit 6 |
Typical Applications
PIC16C55-XTI/SO is suitable for 7 applications: Simple Embedded Control Tasks, Low-Cost Consumer Appliance Controllers, Industrial Sensor Interface Modules, Legacy Replacement / Pin-Compatible Retrofit, Educational 8-bit RISC Learning Platforms, Standalone Battery-Powered Timer / Sequencer, OTP Volume Production (Cost-Optimized Single-Program Builds).
Simple Embedded Control Tasks
The PIC16C55-XTI/SO's 768-byte OTP program memory, 20 I/O pins, and 4 MHz RISC core make it a strong fit for simple embedded control tasks where deterministic timing and low cost matter more than memory size. According to the PIC16C5X family datasheet, the 12-bit instruction set delivers 2:1 code compression over typical 8-bit CISC microcontrollers, so 768 bytes holds meaningful control firmware. Most instructions execute in one cycle (1 microsecond at 4 MHz), giving predictable loop timing for state machines that drive relays, LEDs, or solenoids. The 20 I/O pins comfortably handle a small keypad, a 7-segment display, and a few control outputs in parallel. Unlike Flash MCUs, OTP programming costs less per part and avoids the need for in-circuit programming infrastructure, but the device must be pre-programmed by an external programmer (MPLAB PM3) before PCB stuffing.
Recommended
Low-Cost Consumer Appliance Controllers
The PIC16C55-XTI/SO suits low-cost consumer appliances such as small kitchen timers, battery chargers, and decorative lighting controllers where BOM cost is the dominant design constraint. According to the PIC16C5X datasheet, the industrial -40C to +85C temperature range (the I suffix) allows deployment in moderately harsh consumer environments. The 4 MHz XT oscillator grade supports an inexpensive 4 MHz crystal or ceramic resonator as the clock source, keeping the BOM minimal at two load capacitors and one resonator. The 24 bytes of RAM constrain stack depth, but for linear control loops without recursion this is sufficient. OTP program memory prevents field firmware tampering - useful for safety certifications on consumer products. Use a single 100 nF decoupling cap on VDD and watch-dog timer (WDT) enabled in firmware for unattended appliance safety.
Recommended
Industrial Sensor Interface Modules
The PIC16C55-XTI/SO works well in industrial sensor interface modules that read a small number of digital or slowly-varying analog signals and translate them into simple control outputs. According to the PIC16C5X datasheet, the 8-bit TMR0 counter can be used as a basic event counter or time-base for sensor polling, and the 20 I/O pins allow multiple sensors to be polled in sequence without external muxes. Industrial temperature grade and wide 3.0-6.0V supply tolerance support 5V industrial backplanes or 24V systems with an external regulator. The OTP memory prevents accidental firmware corruption in noisy industrial environments where field firmware updates would risk reliability. For analog sensors requiring an ADC, an external ADC or a different MCU family should be paired because the PIC16C55-XTI/SO has no on-chip analog peripherals.
Recommended
Legacy Replacement / Pin-Compatible Retrofit
The PIC16C55-XTI/SO is the canonical drop-in replacement for any 28-pin PIC16C5X family part that has gone obsolete or out of stock, particularly older PIC16C55, PIC16C55-XT, or PIC16C55-RC designs. According to the Microchip 28-pin PICmicro Pin and Code Compatibility Chart, the entire PIC16C5X 28-pin family shares the same SOIC-28 pinout, instruction set, and programming interface. This means a legacy PCB designed for any 28-pin PIC16C5X variant can accept the PIC16C55-XTI/SO without any board rework - only firmware must be checked for oscillator grade (XT vs RC vs HS vs LP) and temperature grade (industrial I vs commercial) compatibility. The OTP memory means existing programmed parts can be sourced as a one-to-one replacement.
Recommended
Educational 8-bit RISC Learning Platforms
The PIC16C55-XTI/SO's simple RISC architecture with only 33 instructions makes it an excellent educational vehicle for teaching 8-bit microcontroller fundamentals. According to Microchip documentation, the PIC16C5X instruction set fits on a single page and is one of the smallest in any commercial MCU family, allowing students to learn assembly programming quickly. The 28-SOIC package is breadboard-friendly with an SOIC-to-DIP adapter board. The OTP memory forces students to verify code on simulator/emulator before programming, building good engineering discipline. The industrial temperature grade and robust CMOS design tolerate student mishandling. Schools and training labs benefit from the part's low cost and Microchip's free MPLAB IDE toolchain, which supports the PIC16C5X family.
Recommended
Standalone Battery-Powered Timer / Sequencer
The PIC16C55-XTI/SO can serve as a standalone battery-powered timer or sequencer when paired with a low-power crystal and the LP oscillator grade variant. According to the PIC16C5X datasheet, sleep mode current is below 1 microA, allowing years of battery life from a coin cell when the MCU wakes only periodically via WDT. The 20 I/O pins allow direct drive of multiple loads in a defined sequence, with each I/O sourced/sunk at standard CMOS levels. XT oscillator grade with a 32.768 kHz crystal can be used for real-time-clock-like time bases if software compensation is added. The OTP memory prevents accidental reprogramming that could disrupt critical timing sequences.
Recommended
OTP Volume Production (Cost-Optimized Single-Program Builds)
The PIC16C55-XTI/SO's OTP memory is well-suited to high-volume single-program production where firmware is fixed and validated, such as toys, single-function appliances, and disposable consumer devices. According to Microchip's OTP pricing model, OTP parts cost less than equivalent Flash parts because they skip the Flash test and erase circuitry. The 28-SOIC package supports automated pick-and-place assembly. The 4 MHz XT oscillator grade handles typical control firmware timing with comfortable margin. Industrial temperature grade (I suffix) allows global product distribution without regional derating. Programming is performed by MPLAB PM3 or contract manufacturer on a gang programmer before SMT placement.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C55-XTI/SO — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C55T-XTI/SO | PIC16C55T-RCI/SO | PIC16C55T-LPI/SO | PIC16C55T-HSI/SO | PIC16C55T-HSE/SO | PIC16C55-RCI/SO |
|---|---|---|---|---|---|---|---|
| Package | 28-SOIC (wide) | 28-SOIC (wide) | 28-SOIC (wide) | 28-SOIC (wide) | 28-SOIC (wide) | 28-SOIC (wide) | 28-SOIC (wide) |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Oscillator Grade | XT (crystal/resonator) | XT | RC (low-cost) | LP (low-power) | HS (high-speed) | HS (high-speed) | RC (low-cost) |
| Program Memory | 768 B OTP | 768 B OTP | 768 B OTP | 768 B OTP | 768 B OTP | 768 B OTP | 768 B OTP |
| Max Clock Frequency | 4 MHz | 4 MHz | 4 MHz | 4 MHz | 4 MHz | 4 MHz | 4 MHz |
| Operating Temperature | -40C to +85C (Industrial) | -40C to +85C (Industrial) | -40C to +85C (Industrial) | -40C to +85C (Industrial) | -40C to +85C (Industrial) | -40C to +125C (Extended Industrial) | -40C to +85C (Industrial) |
| I/O Pins | 20 | 20 | 20 | 20 | 20 | 20 | 20 |
| RAM | 24 B | 24 B | 24 B | 24 B | 24 B | 24 B | 24 B |
Key Differentiators
- Industrial temperature range standard on this XTI variant (vs PIC16C55-XT/SO (commercial 0C-70C))
- 4 MHz XT oscillator grade optimized for low-cost crystals (vs PIC16C55T-HSI/SO (HS grade for >4 MHz))
- Same-die compatibility across entire PIC16C5X 28-pin family (vs PIC16C558-20/SO (enhanced variant))
Design Notes
Place a 0.1 microF decoupling capacitor as close as possible to the VDD pin (pin 24) with the ground return to VSS (pin 23). For 28-SOIC wide-body layouts, use a ground pour under the part and connect VSS to the pour with multiple vias. The 4 MHz XT oscillator requires 22-33 pF load capacitors on OSC1 (pin 16) and OSC2 (pin 17); keep crystal traces short and surrounded by ground pour to avoid coupling noise into the oscillator stage.
The PIC16C55-XTI/SO has only a 2-level hardware stack, meaning nested CALLs deeper than 2 will overwrite the return address and cause a firmware fault. Estimated: at 4 MHz with 1 microsecond instruction cycle, this means control flow must avoid nested subroutines more than 1 level deep, or use iterative state-machine coding. Also note that the XT oscillator grade requires a crystal or ceramic resonator - using an external clock source into OSC1 with the wrong drive strength can cause oscillator failure.
All 20 I/O pins share the 5V VDD supply, so any input exceeding VDD + 0.3V will forward-bias the ESD clamp and inject current. For industrial sensor interfaces where signals may exceed 5V, add external series resistors (1-10 kohm) and clamp diodes. The MCLR reset pin (pin 26) requires a 10-50 kohm pull-up to VDD; leaving it floating causes intermittent reset behavior in noisy environments. PORTA pins RA4 (T0CKI) is an open-drain output and requires an external pull-up if used as a digital output.
Estimated: the PIC16C55-XTI/SO dissipates approximately 20 mW at 4 MHz / 5V / 100% CPU utilization, well within the 28-SOIC thermal budget (theta_JA approximately 70-80 C/W on a standard 4-layer PCB with copper pour). Industrial -40C to +85C operation is supported without special thermal measures. In enclosed housings with no airflow, derate by 20% to account for thermal accumulation. Sleep mode current is below 1 microA at room temperature and dominates battery-life calculations in low-duty-cycle designs.
Compliance Information
RoHS status not explicitly stated in the verified distributor snippets; marked unknown per Data Authenticity Rule. REACH compliant per FindMyChip product page. AEC-Q100 not applicable - this is a general-purpose industrial-grade MCU, not an automotive-qualified part.
