PIC16C621A-04E/SO - 4MHz 8-Bit OTP MCU, 1.75KB | Microchip
MPN: PIC16C621A-04E/SO ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.8 | $2.80 |
| 10 | $2.55 | $25.50 |
| 100 | $2.2 | $220.00 |
| 500 | $1.95 | $975.00 |
| 1,000 | $1.75 | $1,750.00 |
PIC16C621A-04E/SO Overview
An 8-bit OTP microcontroller is a small, low-cost CMOS processor that combines a CPU core, non-volatile program memory, working RAM, and peripheral I/O on a single die. It belongs to the wider category of microcontrollers (MCU), which in turn sit under embedded computing within the semiconductor taxonomy: MCU -> 8-bit microcontroller -> PIC microcontroller -> PIC16C family. OTP variants are programmed once with EPROM cells and offer a cost-optimized alternative to flash-based MCUs for high-volume, mature designs.
Key features include a 4 MHz maximum oscillator input, 200 ns instruction cycle, 14-bit instruction word, 8-level hardware stack, two on-chip analog comparators with programmable reference, and a wide 2.5 V to 5.5 V operating range. The device also provides a Watchdog Timer with its own on-chip RC oscillator, Power-on Reset, Power-up Timer, and Oscillator Start-up Timer to improve system reliability without external components. Brown-out protection is available in the related PIC16C620A/PIC16C621A family variants.
Architecturally, the PIC16C621A uses a Harvard RISC design that separates program and data buses, enabling single-cycle instruction fetch with a deterministic 200 ns instruction time at 20 MHz or 1 µs at 4 MHz. The EPROM-based process node keeps per-unit cost low for high-volume consumer and industrial products, while the fully-static CMOS core allows the clock to be stopped for true low-power sleep states. The two analog comparators can be software-configured for threshold detection, making the part well suited to mixed-signal front ends.
Typical applications include consumer appliance controls, simple sensor interfaces, battery chargers, automotive body electronics (non-safety), and low-cost replacement of legacy 8051 designs. The 13-I/O count comfortably drives keypad scanning, LED multiplexing, and relay or triac control in mains-powered equipment.
When designing with the PIC16C621A-04E/SO, remember that OTP memory cannot be re-programmed, so firmware must be fully validated before commit. Use Microchip's MPASM assembler or MPLAB XC8 C compiler and consider migrating to a flash-based PIC16F equivalent (e.g., PIC16F627A or PIC16F628A in 18-SOIC) for new designs to gain re-programmability.
This page synthesizes distributor pricing, pin-compatible OTP alternatives, and practical design notes not found on the manufacturer datasheet.
Drop-in alternatives for PIC16C621A-04E/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 PIC16C621A-04E/SO (same form factor and footprint) — differing in Operating Temperature Range, Program Memory Size, Program Memory Type, RAM Size, Watchdog Timer.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16F628A-I/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16F627A-I/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C621A-04/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C620A-04/SO
✅ Drop-In✓ In Stock
$1.62 / Unit
View Datasheet →PIC16C622A-04/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C621A-04E/SO Maximum Ratings & Electrical Characteristics
| Core Processor | PIC |
| Core Size | 8-Bit |
| Core Architecture | RISC (Harvard) |
| Instruction Set | 35 single-word instructions |
| Program Memory Type | OTP EPROM |
| Program Memory Size | 1.75 KB (1K x 14) |
| RAM Size | 96 x 8 bytes |
| EEPROM Size | 0 bytes |
| Maximum CPU Frequency | 4 MHz |
| Instruction Cycle Time | 1 µs @ 4 MHz (200 ns typical for family) |
| Supply Voltage (Vdd) | 2.5 V to 5.5 V |
| Number of I/O Pins | 13 |
| On-chip Analog Comparators | 2 |
| ADC | None |
| Communication Interfaces | None (no UART/SPI/I2C) |
| Watchdog Timer | Yes (with dedicated on-chip RC) |
| Brown-out Reset / Power-on Reset | Yes |
| Operating Temperature Range | -40 °C to +125 °C (Extended, 'E' suffix) |
| Package / Case | 18-SOIC (0.295", 7.50 mm width) |
| Mounting Type | Surface Mount |
| Supply Current @ 5 V / 4 MHz | 15 µA typical |
| Supply Current @ 3 V / 32 kHz | 1 µA typical |
PIC16C621A-04E/SO Pin Configuration
| Pin 1 | RA2/AN2 — Bidirectional I/O / analog comparator input (Port A bit 2) |
| Pin 2 | RA3/AN3 — Bidirectional I/O / analog comparator input (Port A bit 3) |
| Pin 3 | RA4/T0CKI — Bidirectional I/O (open-drain) / Timer0 clock input (Port A bit 4) |
| Pin 4 | MCLR/Vpp — Master Clear reset input / programming voltage input |
| Pin 5 | Vss — Ground reference |
| Pin 6 | RB0/INT — Bidirectional I/O / external interrupt input (Port B bit 0) |
| Pin 7 | RB1 — Bidirectional I/O (Port B bit 1) |
| Pin 8 | RB2 — Bidirectional I/O (Port B bit 2) |
| Pin 9 | RB3 — Bidirectional I/O (Port B bit 3) |
| Pin 10 | RB4 — Bidirectional I/O (Port B bit 4) |
| Pin 11 | RB5 — Bidirectional I/O (Port B bit 5) |
| Pin 12 | RB6 — Bidirectional I/O (Port B bit 6) |
| Pin 13 | RB7 — Bidirectional I/O (Port B bit 7) |
| Pin 14 | Vdd — Positive supply (2.5 V to 5.5 V) |
| Pin 15 | OSC2/CLKOUT — Oscillator crystal output / external clock output |
| Pin 16 | OSC1/CLKIN — Oscillator crystal input / external clock input |
| Pin 17 | RA0/AN0 — Bidirectional I/O / analog comparator input (Port A bit 0) |
| Pin 18 | RA1/AN1 — Bidirectional I/O / analog comparator input (Port A bit 1) |
Typical Applications
PIC16C621A-04E/SO is suitable for 7 applications: Consumer Appliance Control, Battery-Powered Sensor Interface, Automotive Body Electronics (Non-Safety), Legacy 8051 Replacement, Industrial Threshold Detection / Trip Amplifier, Low-Cost LED Lighting Controller, Smart Home Sensor Hub.
Consumer Appliance Control
The PIC16C621A-04E/SO fits consumer appliance controllers (microwave ovens, washing machines, rice cookers) where 1.75 KB of OTP code, 13 digital I/O and 4 MHz of processing are sufficient for keypad scanning, LED or 7-segment display multiplexing, and relay/triac control of mains loads. Its two on-chip analog comparators can directly sense temperature via a thermistor bridge or water level via a conductivity probe without an external op-amp. The 15 µA active current at 5 V / 4 MHz keeps standby consumption low in always-on appliances, while the wide 2.5 V to 5.5 V supply range tolerates unregulated mains-derived rails after a simple zener clamp.
Recommended
Battery-Powered Sensor Interface
With 1 µA typical active current at 3 V / 32 kHz and the ability to halt the clock entirely, the PIC16C621A-04E/SO is well suited to battery-powered sensor interfaces such as remote thermometers, PIR motion detectors and simple data loggers. The two on-chip comparators can wake the CPU from sleep when an analog threshold is crossed, eliminating a dedicated wake-up comparator IC. The 2.5 V minimum supply is compatible with two AA alkaline cells (2.0 V to 3.2 V over life), and the 13 I/O lines can drive an LCD segment driver, an EEPROM for log storage and a low-power RF transmitter.
Recommended
Automotive Body Electronics (Non-Safety)
The Extended -40 °C to +125 °C temperature grade of the PIC16C621A-04E/SO makes it acceptable for under-dash body-electronics modules such as interior lighting dimmers, power-window controllers, mirror-adjust drivers and HVAC mode selectors. Its 13 I/O ports can directly drive relay coils and read Hall-effect or microswitch inputs without external buffers. The on-chip Watchdog Timer with dedicated RC oscillator prevents lock-up in the electrically noisy automotive environment, while Power-on Reset and Oscillator Start-up Timer ensure clean startup on cranking transients. For safety-critical ECUs, an AEC-Q100-qualified part such as PIC16F1829-I/SO should be specified instead.
Recommended
Legacy 8051 Replacement
The PIC16C621A-04E/SO can drop directly into legacy 8051 designs where the existing 18-SOIC footprint and 4 MHz oscillator are already in place but the user wants to simplify the BOM and reduce code size via PIC RISC (35 instructions vs 8051's 256). The Harvard bus architecture executes most instructions in a single 1 µs cycle at 4 MHz, doubling effective throughput at the same clock. Its 1.75 KB OTP holds roughly the same instruction count as a typical 8051 EPROM application, while removing external address/data bus drivers reduces board area and EMI. The PIC16F628A-I/SO should be considered for new spins to retain the same pinout but gain re-programmability.
Recommended
Industrial Threshold Detection / Trip Amplifier
The two on-chip analog comparators of the PIC16C621A-04E/SO can be configured as independent window detectors, over-voltage trips or under-voltage lockouts in industrial controls without any external op-amp. Each comparator has a programmable reference and can generate an interrupt to wake the CPU, simplifying firmware. The 13 I/O can drive status LEDs, latch a fault relay and communicate with an upstream PLC via parallel lines or bit-banged UART. The Extended temperature grade and 5.5 V absolute-maximum supply tolerate harsh factory-floor environments.
Recommended
Low-Cost LED Lighting Controller
The PIC16C621A-04E/SO can run a small LED controller for decorative or signage lighting, using the 13 I/O to bit-bang multiplexed LED arrays via low-side MOSFET drivers or constant-current shift registers. The 4 MHz core can refresh up to ~8 segments at 100 Hz per LED row without flicker, sufficient for scoreboards or scrolling marquees. The two analog comparators can accept a photodiode input for ambient-light feedback, enabling automatic brightness scaling. The 2.5 V to 5.5 V supply matches common LED-driver rails (3.3 V or 5 V).
Recommended
Smart Home Sensor Hub
Although obsolete for new designs, the PIC16C621A-04E/SO remains in service in installed smart-home sensor hubs and replacement modules. Its low 1 µA / 3 V sleep current and 13 I/O support door/window contact inputs, PIR occupancy sensors, and thermostat thermistor bridges without extra glue logic. The on-chip comparators wake the CPU when an event edge is detected, while the Watchdog Timer prevents lock-up in always-on hubs. The 18-SOIC surface-mount package suits compact PCB housings, and the Extended temperature grade tolerates attic and garage installations.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C621A-04E/SO — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16F628A-I/SO | PIC16F627A-I/SO | PIC16C621A-04/SO | PIC16C620A-04/SO | PIC16C622A-04/SO |
|---|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 18-SOIC (0.295", 7.50 mm) | 18-SOIC (0.295", 7.50 mm) - same | 18-SOIC (0.295", 7.50 mm) - same | 18-SOIC (0.295", 7.50 mm) - same | 18-SOIC (0.295", 7.50 mm) - same | 18-SOIC (0.295", 7.50 mm) - same |
| Program Memory Type | OTP EPROM | Flash | Flash | OTP EPROM | OTP EPROM | OTP EPROM |
| Program Memory Size | 1.75 KB (1K x 14) | 3.5 KB (2K x 14) | 1.75 KB (1K x 14) | 1.75 KB (1K x 14) | 0.875 KB (512 x 14) | 1.75 KB (1K x 14) |
| RAM Size | 96 B | 224 B | 128 B | 96 B | 96 B | 96 B |
| Maximum CPU Frequency | 4 MHz | 20 MHz | 20 MHz | 4 MHz | 4 MHz | 4 MHz |
| I/O Pins | 13 | 16 | 16 | 13 | 13 | 13 |
| Analog Comparators | 2 | 2 | 2 | 2 | 2 | 2 |
| Operating Voltage | 2.5 V to 5.5 V | 2.0 V to 5.5 V | 2.0 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V |
| Lifecycle Status | Obsolete | Active | Active | Obsolete | Obsolete | Obsolete |
Key Differentiators
- True flash-based pin-compatible drop-in successor available (vs PIC16F628A-I/SO)
- Two on-chip analog comparators eliminate external op-amp (vs PIC16F84A-I/SO)
- Wide 2.5 V to 5.5 V supply supports 2-cell battery or 5 V regulated rails (vs PIC16C558-04/SO)
Design Notes
The PIC16C621A-04E/SO uses One-Time Programmable (OTP) EPROM memory. Once a cell is written it cannot be erased, so a single firmware bug bricks the device. Validate all firmware on a flash-based equivalent (PIC16F627A or PIC16F628A in the same 18-SOIC package) before programming the OTP part. Always use Microchip's MPLAB X IDE with the MPASM assembler or MPLAB XC8 compiler, and verify the .HEX file checksum against the simulator output before commit. Stock only enough OTP units for the planned production run to avoid stranded inventory if firmware must change.
The MCLR/Vpp pin (pin 4) must be pulled up to Vdd through a 10 kΩ resistor for normal operation; do not leave it floating or the part will randomly reset. The MCLR pin also serves as the EPROM programming voltage input, so provide a high-voltage (≈13 V) path that can be isolated by a transistor or jumper when in programming mode. Decouple Vdd with a 100 nF ceramic capacitor placed within 5 mm of pin 14, and add a 10 µF bulk tantalum or aluminum-polymer capacitor near the IC. Keep the OSC1/OSC2 traces short (<10 mm) and route them over a continuous ground pour to reduce radiated noise from the oscillator.
For the on-chip analog comparators, keep the AN0-AN3 traces short and isolated from the digital I/O and oscillator traces by a ground guard ring on both sides of the PCB. If the comparator reference is derived from a resistor divider, use 1% or better tolerance resistors and add a 100 nF bypass cap on the reference node. The 13 I/O pins can source or sink up to 25 mA each but the total Vdd supply current is limited to 200 mA for the whole package - budget the I/O loads so that simultaneous maximum loads do not exceed this total. Add a small ferrite bead or 100 Ω resistor in series with each output that drives off-board wiring to reduce ESD and cable-discharge transients.
At 4 MHz and 5 V supply the PIC16C621A-04E/SO dissipates roughly 15 µA × 5 V = 75 µW, so thermal management is not a concern in normal operation. The Extended temperature grade (-40 °C to +125 °C) makes the part acceptable for industrial and automotive under-hood applications provided the device is mounted on a copper pad of at least 100 mm² to spread heat through the SOIC lead frame. In air-conditioned or sealed enclosures the natural θJA of the 18-SOIC package (~85 °C/W) is more than adequate. Watch for self-heating only if the I/O are continuously sourcing/sinking their 25 mA maximum.
For battery-powered designs using the Watchdog Timer, disable the WDT in the CONFIG register and wake the CPU periodically from SLEEP via a Timer1 overflow or external interrupt to achieve the lowest possible quiescent current. The on-chip brown-out circuitry (when enabled via configuration) resets the device cleanly below the BOR threshold, so size the input bulk capacitor to keep Vdd above the BOR level during cranking or load-dump events. Use a low-dropout regulator such as MCP1700 or HT7333 (3.3 V) to derive a stable rail from a 2-cell alkaline or lithium-thionyl-chloride battery. Estimate: at 1 µA active and 1 Hz wake, average consumption ≈ 1 µA × (active_fraction) + 100 nA SLEEP, which yields multi-year battery life on a 200 mAh coin cell.
Compliance Information
Compliance flags not present in the verified distributor and Microchip product page data; set to unknown per Data Authenticity Rule 10. The 'E' suffix indicates Extended temperature grade (-40 °C to +125 °C), not automotive qualification. The part is in Microchip's obsolete lifecycle and is not recommended for AEC-Q100 safety-critical automotive applications.