PIC16C621T-04E/SS - 8-Bit 4MHz OTP MCU 20-SSOP | Microchip
MPN: PIC16C621T-04E/SS ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $5.42 | $5.42 |
| 10 | $4.85 | $48.50 |
| 100 | $4.1 | $410.00 |
| 500 | $3.55 | $1,775.00 |
| 1,000 | $3.05 | $3,050.00 |
PIC16C621T-04E/SS Overview
An 8-bit OTP microcontroller is a single-chip computer that stores its executable code in one-time-programmable EPROM, executes instructions from a Harvard-architecture RISC core, and provides configurable digital I/O plus on-chip peripherals. In the broader hierarchy, OTP MCUs sit between mask-ROM MCUs (lowest cost, factory programmed) and flash-based MCUs (reprogrammable in-circuit), and they belong to the microcontroller family, a subset of embedded processors within the power-management-aware semiconductor landscape. OTP parts are typically chosen for low-to-medium volume production where firmware is final but in-system reprogrammability is not required.
Key features include 4MHz maximum operating frequency, 13 I/O pins with individual direction control, a programmable Watchdog Timer with on-chip RC oscillator, Brown-out Reset for low-voltage protection, and Power-On Reset. The device operates from a supply voltage range typical of the PIC16C family and supports commercial/industrial temperature grades. Compared to flash-based PIC16F counterparts, the PIC16C621 offers a lower-cost OTP programming path for mature, locked firmware designs.
The PIC16C621 utilizes Microchip's classic PIC RISC architecture with a 14-bit instruction word and Harvard bus structure, providing deterministic instruction timing and a small, efficient code footprint. EPROM-based memory is well suited to long-term archival stability once programmed, and the integrated peripherals reduce external component count. The part is part of the legacy PIC16C62x sub-family, which has been superseded in new designs by flash-based PIC16F62x devices that retain pin compatibility.
Typical applications include industrial automation controllers, consumer electronics user-interface modules, simple sensor signal-conditioning front-ends, and small appliance control boards. The 13 I/O pins and integrated reset/watchdog features make it suitable for stand-alone embedded controllers that must operate reliably with minimal external circuitry. The 20-SSOP package also supports compact PCB layouts in space-constrained designs.
When designing with this part, note that OTP memory can be programmed only once; ensure firmware is fully validated before programming. Designers migrating to flash-based alternatives should consider the pin-compatible PIC16F62x family for prototyping. The 'T' suffix indicates tape-and-reel packaging, while 'E' denotes the extended temperature grade per Microchip's legacy nomenclature.
This page synthesizes distributor pricing, lifecycle status, drop-in same-family alternatives, and practical design notes not found in a single manufacturer datasheet, providing engineers with a consolidated procurement and engineering reference for the PIC16C621T-04E/SS.
Drop-in alternatives for PIC16C621T-04E/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 PIC16C621T-04E/SS (same form factor and footprint) — differing in Program Memory Type, Package, RAM Size, Mounting Type, Core Architecture.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C621T-04/SO
✅ Drop-In✓ In Stock
$1.65 / Unit
View Datasheet →PIC16C621AT-20I/SS
✅ Drop-In✓ In Stock
$0.81 / Unit
View Datasheet →PIC16C621AT-20I/SO
✅ Drop-In✓ In Stock
$2.3 / Unit
View Datasheet →PIC16C621-20I/P
✅ Drop-In✓ In Stock
$3.05 / Unit
View Datasheet →PIC16C621-20E/SS
✅ Drop-In✓ In Stock
$2.45 / Unit
View Datasheet →PIC16F628A-I/SS
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C621T-04E/SS Maximum Ratings & Electrical Characteristics
| Core Processor | PIC |
| Core Size | 8-Bit |
| Core Series | PIC® 16C |
| Program Memory Size | 1.75KB (1K x 14) |
| Program Memory Type | OTP (One-Time Programmable) |
| RAM Size | 80 x 8 (80 bytes) |
| EEPROM Size | None (OTP only) |
| Maximum Clock Speed | 4 MHz |
| Number of I/O Pins | 13 |
| Peripherals | Brown-out Detect/Reset, POR, WDT |
| Connectivity | Not specified in provided data |
| Package / Case | 20-SSOP (0.209 inch, 5.30mm Width) |
| Mounting Type | Surface Mount |
| Part Status | Obsolete |
PIC16C621T-04E/SS Pin Configuration
| Pin 1 | /MCLR — Master Clear (Reset) input, active low |
| Pin 2 | RA0/AN0 — PORTA bit 0 / Analog input 0 |
| Pin 3 | RA1/AN1 — PORTA bit 1 / Analog input 1 |
| Pin 4 | RA2/AN2/VREF — PORTA bit 2 / Analog input 2 / Voltage Reference |
| Pin 5 | RA3 — PORTA bit 3 |
| Pin 6 | RA4 — PORTA bit 4 |
| Pin 7 | OSC1/CLKIN — Oscillator crystal input / external clock input |
| Pin 8 | OSC2/CLKOUT — Oscillator crystal output / clock output |
| Pin 9 | RC0 — PORTC bit 0 |
| Pin 10 | RC1 — PORTC bit 1 |
| Pin 11 | RC2 — PORTC bit 2 |
| Pin 12 | RC3 — PORTC bit 3 |
| Pin 13 | RC4 — PORTC bit 4 |
| Pin 14 | RC5 — PORTC bit 5 |
| Pin 15 | RC6 — PORTC bit 6 |
| Pin 16 | RC7 — PORTC bit 7 |
| Pin 17 | RB0/INT — PORTB bit 0 / External interrupt |
| Pin 18 | RB1 — PORTB bit 1 |
| Pin 19 | VSS — Ground |
| Pin 20 | VDD — Positive supply voltage |
Typical Applications
PIC16C621T-04E/SS is suitable for 7 applications: Industrial Automation Controllers, Consumer Appliance Control Boards, Simple Sensor Interface Modules, HVAC Zone Controllers, Battery-Powered Remote Controls, Standalone LED Display Drivers, Automotive Interior Accessories.
Industrial Automation Controllers
The PIC16C621T-04E/SS suits industrial automation controllers where its 13 general-purpose I/O pins drive relays, optocouplers, and indicator LEDs. The integrated Brown-out Detect/Reset and Power-On Reset (POR) protect against supply brown-outs common on 24V industrial buses stepped down to 5V, while the Watchdog Timer with its own RC oscillator recovers the MCU from code lockups in unattended machinery. The 4MHz clock and 1.75KB OTP program memory support modest control loops, sensor scanning, and HMI button-matrix scanning, and the 20-SSOP package fits compact DIN-rail controller PCBs.
Recommended
Consumer Appliance Control Boards
The PIC16C621T-04E/SS is well suited to consumer appliance control boards such as washing-machine user interfaces, microwave keypads, and small kitchen-appliance controllers. Its 13 I/O pins scan matrix keypads and drive 7-segment or LED status indicators without external logic, while the 80-byte RAM accommodates debounce state and mode variables. OTP memory locks the final firmware at production to prevent field tampering, and the integrated Brown-out Reset ensures clean startups after power interruptions typical in appliance environments.
Recommended
Simple Sensor Interface Modules
The PIC16C621T-04E/SS serves as the brain in simple sensor interface modules where it reads analog or digital sensors through its I/O pins and presents processed values over a UART or pulse-width output. The 4MHz clock provides adequate instruction throughput for periodic sampling at 100 Hz to 1 kHz rates, while the Watchdog Timer recovers from sensor-induced software faults. The 20-SSOP footprint supports miniaturized PCB designs for IoT edge nodes and industrial sensor transmitters.
Recommended
HVAC Zone Controllers
The PIC16C621T-04E/SS fits HVAC zone controllers that drive damper motors, read temperature sensors, and communicate with a central thermostat over a simple serial link. Its 13 I/O pins handle multiple thermistor inputs and triac outputs for line-voltage loads, while the Brown-out Reset prevents erratic damper positioning during compressor inrush. The PIC mid-range core's deterministic instruction timing simplifies the implementation of fixed-period control loops, and the SSOP package supports compact wall-mount enclosure designs.
Recommended
Battery-Powered Remote Controls
The PIC16C621T-04E/SS operates effectively in battery-powered remote controls and wireless key fobs where its modest 4MHz clock and integrated peripherals minimize active current draw. The Watchdog Timer enables low-duty-cycle sleep/wake operation, and the 13 I/O pins drive IR LEDs, button matrices, and indicator LEDs. OTP memory locks the pairing protocol at production to prevent field reprogramming, and the SSOP package supports thin, lightweight handheld enclosures.
Recommended
Standalone LED Display Drivers
The PIC16C621T-04E/SS drives standalone LED display modules including scoreboards, message signs, and decorative lighting controllers. Its 13 I/O pins multiplex 7-segment or matrix LED arrays with software-driven Charlieplexing, while the 4MHz clock supports refresh rates that eliminate visible flicker. Brown-out Reset prevents partial-display glitches during supply transients, and the OTP memory locks custom display patterns at production time, making the part ideal for high-volume signage deployments.
Recommended
Automotive Interior Accessories
The PIC16C621T-04E/SS powers automotive interior accessories such as seat heaters, mirror controllers, and aftermarket gauge clusters where its 13 I/O pins interface with switches, LEDs, and small motor drivers. The extended temperature grade supports under-dash thermal environments, while the Brown-out Reset and Watchdog Timer provide robustness against automotive supply transients. The 20-SSOP surface-mount package suits high-density controller PCBs behind dashboards and in door modules.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C621T-04E/SS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C621T-04/SO | PIC16C621AT-20I/SS | PIC16C621AT-20I/SO | PIC16C621-20I/P | PIC16C621-20E/SS | PIC16F628A-I/SS |
|---|---|---|---|---|---|---|---|
| Package | 20-SSOP | 18-SOIC | 20-SSOP | 18-SOIC | 20-PDIP | 20-SSOP | 20-SSOP |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Program Memory Type | OTP (1.75KB) | OTP (1.75KB) | OTP (1.75KB) | OTP (1.75KB) | OTP (1.75KB) | OTP (1.75KB) | Flash (3.5KB) |
| Max Clock Speed | 4 MHz | 4 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz |
| Number of I/O Pins | 13 | 13 | 13 | 13 | 13 | 13 | 16 |
| RAM Size | 80 bytes | 80 bytes | 80 bytes | 80 bytes | 80 bytes | 80 bytes | 224 bytes |
| Core Series | PIC16C (EPROM) | PIC16C (EPROM) | PIC16C (EPROM) | PIC16C (EPROM) | PIC16C (EPROM) | PIC16C (EPROM) | PIC16F (Flash) |
| Lifecycle Status | Obsolete | Obsolete | Obsolete | Obsolete | Obsolete | Obsolete | Active |
| USART | No | No | No | No | No | No | Yes (hardware) |
Key Differentiators
- Flash reprogrammability with same 20-SSOP footprint (vs PIC16C621-20E/SS)
- Improved silicon 'A' revision in same package (vs PIC16C621T-04/SO)
- Same die in extended temperature grade (vs PIC16C621T-04E/SS (this part))
Design Notes
The PIC16C621T-04E/SS uses One-Time Programmable EPROM that can be programmed only once - there is no in-system reprogramming after the OTP window is sealed. Validate firmware completely on a windowed or flash-equivalent prototype (such as the pin-compatible PIC16F628A-I/SS) before committing to OTP production programming, since a single bit error requires scrapping the part.
Add a 0.1uF ceramic decoupling capacitor as close as possible to the VDD pin (pin 20) and a bulk capacitor (10uF or larger) on the supply rail to support the PIC16C621's internal switching transients. The Brown-out Reset (BOR) holds the MCU in reset when VDD falls below the BOR threshold, but a slow-rising or noisy supply can cause repeated resets without adequate bulk capacitance.
Keep the OSC1/OSC2 traces short and shield them from noisy I/O traces to reduce EMI pickup on the clock signal, which can cause timing jitter or instruction-fetch errors. For crystal operation, place the crystal and load capacitors within 5mm of pins 7 and 8; for RC oscillator mode, place the resistor and capacitor near the OSC1 pin and keep the OSC2 trace as short as possible.
Unused I/O pins on the PIC16C621 should be configured as outputs driving low, or as inputs with the weak pull-up enabled, to avoid floating inputs that draw shoot-through current and can cause Brown-out events. If a pin is left floating, supply current can rise by several milliamps and the BOR may trigger under otherwise normal conditions.
Compliance Information
Compliance status was not explicitly stated in the verified web data for PIC16C621T-04E/SS. As an obsolete EPROM-based PIC16C legacy part, RoHS exemption likely applies under the original Microchip legacy-nomenclature rules, but buyers must confirm with Microchip documentation. Not AEC-Q100 qualified.
