PIC16C621AT-20I/SS - 8-Bit 20MHz OTP MCU, 1.75KB | Microchip
MPN: PIC16C621AT-20I/SS ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.28 | $1.28 |
| 10 | $1.22 | $12.20 |
| 100 | $1.05 | $105.00 |
| 500 | $0.92 | $460.00 |
| 1,000 | $0.81 | $810.00 |
PIC16C621AT-20I/SS Overview
An 8-bit microcontroller (MCU) is a single-chip computer that combines an 8-bit CPU, program memory, data RAM, and peripheral I/O on one die. PIC microcontrollers use a RISC Harvard architecture with separate program and data buses, allowing instruction fetch and operand read in a single cycle. The PIC16C62x family sits at the entry-level of Microchip's mid-range PIC16 lineup, designed for compact, cost-sensitive embedded control where deterministic timing, low pin count, and small code footprint matter more than raw throughput.
The PIC16C621A core executes 35 single-word instructions in 200 ns at 20 MHz (100 ns instruction cycle at 20 MHz oscillator). On-chip peripherals include an 8-bit timer/counter (TMR0) with an 8-bit prescaler, a Watchdog Timer with its own on-chip RC oscillator for reliable reset, and a 16-bit Capture/Compare/PWM (CCP) module. Two comparators with programmable reference are integrated for analog signal conditioning, eliminating the need for external op-amps in threshold-detection circuits. The device supports in-circuit serial programming (ICSP) through RB6 and RB7, enabling field updates without removing the part from the board.
Typical applications include low-cost consumer appliances, security keypads, automotive body electronics sub-modules, sensor interfaces, and battery-powered instrument controllers where the on-chip comparators handle analog thresholding. The 20-SSOP footprint is pin-compatible with several PIC16C62x, PIC16C55x, and PIC16F family devices, allowing a single PCB layout to support multiple firmware variants or migration to flash-based PIC16F parts for prototype-to-production flexibility.
When designing with the PIC16C621A, note that OTP memory is one-time programmable, so firmware must be fully validated before programming. Choose the 'T' tape-and-reel suffix for production volumes and the 'I' industrial temperature grade for -40 C to +85 C operation. Migrating to a flash-based PIC16F621 or PIC16F628 in the same 20-SSOP footprint gives rework capability at the cost of higher unit price.
This page synthesizes distributor pricing, drop-in same-package alternatives, and practical design notes not found in the manufacturer datasheet alone.
Drop-in alternatives for PIC16C621AT-20I/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 PIC16C621AT-20I/SS (same form factor and footprint) — differing in Operating Temperature, Analog Comparators, Instruction Cycle Time, Core Architecture, Package.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C621A-20E/SS
✅ Drop-In✓ In Stock
$4.12 / Unit
View Datasheet →PIC16C620AT-20/SS
✅ Drop-In✓ In Stock
$2.18 / Unit
View Datasheet →PIC16C620A-20I/SS
✅ Drop-In✓ In Stock
$2.15 / Unit
View Datasheet →PIC16F628-I/SS
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C621AT-20I/SS Maximum Ratings & Electrical Characteristics
| Program Memory Type | OTP EPROM |
| Program Memory Size | 1.75 KB (1K x 14) |
| Data RAM | 96 bytes |
| CPU Core | PIC16C, 8-bit RISC |
| Instruction Set Size | 35 single-word instructions |
| Max CPU Frequency | 20 MHz |
| Instruction Cycle Time | 200 ns at 20 MHz |
| Supply Voltage (Vdd) | 2.5 V to 5.5 V |
| I/O Pins | 13 |
| Timers | TMR0 (8-bit) with 8-bit prescaler + WDT |
| CCP Modules | 1 x 16-bit Capture/Compare/PWM |
| Analog Comparators | 2 with programmable reference |
| Operating Temperature | -40 C to +85 C (Industrial) |
| Package | 20-pin SSOP (5.2 mm body) |
| Mounting Type | Surface Mount |
| ICSP Programming | Yes (RB6/RB7) |
| RoHS Status | Compliant |
PIC16C621AT-20I/SS Pin Configuration
| Pin 1 | RA2/AN2 — Digital I/O / analog comparator input |
| Pin 2 | RA3/AN3 — Digital I/O / analog comparator input |
| Pin 3 | RA4/T0CKI — Digital I/O / Timer0 clock input |
| Pin 4 | MCLR — Master Clear (reset) input |
| Pin 5 | Vss — Ground |
| Pin 6 | RB0/INT — Digital I/O / external interrupt |
| Pin 7 | RB1 — Digital I/O |
| Pin 8 | RB2 — Digital I/O |
| Pin 9 | RB3 — Digital I/O |
| Pin 10 | RB4 — Digital I/O / interrupt-on-change |
| Pin 11 | RB5 — Digital I/O / interrupt-on-change |
| Pin 12 | RB6/PGC — Digital I/O / ICSP clock |
| Pin 13 | RB7/PGD — Digital I/O / ICSP data |
| Pin 14 | Vdd — Positive supply voltage (2.5 V to 5.5 V) |
| Pin 15 | OSC2/CLKOUT — Oscillator crystal / clock output |
| Pin 16 | OSC1/CLKIN — Oscillator crystal / clock input |
| Pin 17 | RA0/AN0 — Digital I/O / analog comparator input |
| Pin 18 | RA1/AN1 — Digital I/O / analog comparator input |
| Pin 19 | CVREF — Comparator reference voltage output |
| Pin 20 | CCP1 — Capture/Compare/PWM module 1 output |
Typical Applications
PIC16C621AT-20I/SS is suitable for 6 applications: Consumer Appliance Control, Security Keypad and Access Control, Automotive Body Electronics Sub-Modules, Battery-Powered Instrument Controllers, Industrial Sensor Interface Modules, Hobby and Educational Development.
Consumer Appliance Control
The PIC16C621AT-20I/SS suits low-cost consumer appliances such as coffee makers, microwave oven keypads, and small kitchen devices where 1.75 KB of OTP memory holds the firmware comfortably. Its 20 MHz core delivers 5 MIPS, providing ample headroom for keypad scanning, timer logic, and indicator LED multiplexing. The dual on-chip comparators monitor temperature thresholds via NTC thermistor dividers, replacing an external op-amp and reducing BOM cost. The wide 2.5 V to 5.5 V supply range allows direct connection to 3.3 V or 5 V rails from rectified mains adapters, while industrial -40 C to +85 C grading supports both indoor and outdoor appliances such as dehumidifiers. ICSP over RB6/RB7 lets production lines program and verify firmware on-board, eliminating socketed programming steps.
Recommended
Security Keypad and Access Control
In security keypads and access control panels, the PIC16C621AT-20I/SS provides enough I/O and code space to scan a 4x4 matrix keypad, drive status LEDs, and control an electric lock via a relay. With 13 I/O pins, designers can dedicate 8 pins to row/column keypad scanning, 2 to LED drivers, and 1 to the relay driver while retaining serial I/O for external Wiegand-reader communication. The Watchdog Timer with independent on-chip RC oscillator prevents firmware lockup in unattended security installations. The two on-chip analog comparators can supervise the backup-battery voltage and detect tamper-switch closures without additional analog components. Industrial temperature grading ensures the unit operates reliably in unheated vestibules or outdoor enclosures.
Recommended
Automotive Body Electronics Sub-Modules
Within automotive body controllers for window lifters, mirror adjusters, or seat controllers, the PIC16C621AT-20I/SS can handle multiple digital sensor inputs and actuator outputs in a single chip. The 13 I/O pins multiplex limit-switch inputs, Hall-effect sensor feedback, and H-bridge direction control without external logic. The two on-chip comparators detect over-current conditions by sensing a shunt resistor, allowing software-driven shutdown within microseconds of a fault. Industrial -40 C to +85 C operation covers cabin and trunk environments; for under-hood modules Microchip recommends AEC-Q100-qualified PIC16F counterparts. The 20-SSOP package suits space-constrained PCBAs in door modules where thermal copper pours are minimal.
Recommended
Battery-Powered Instrument Controllers
The PIC16C621AT-20I/SS operating from 2.5 V to 5.5 V fits battery-powered portable instruments such as digital calipers, hand-held multimeters, and pocket environmental meters. The low-power SLEEP mode with Watchdog Timer wake-up extends battery life to months in intermittent-use applications. The dual on-chip comparators handle threshold detection for battery voltage monitoring and sensor signal conditioning directly, eliminating an external op-amp. The 96-byte RAM holds sampled readings between display refreshes, and the 1.75 KB OTP memory accommodates full instrument firmware including LCD driving routines. Surface-mount 20-SSOP keeps the device height below 2 mm, suitable for slim industrial gauges.
Recommended
Industrial Sensor Interface Modules
In industrial 4-20 mA loop-powered sensor transmitters or RTD signal conditioners, the PIC16C621AT-20I/SS handles linearization, scaling, and digital output via the 13 available I/O lines. The two on-chip comparators can directly sense the 4-20 mA loop voltage drop across a precision shunt, allowing software calibration without an external ADC. The Watchdog Timer protects against firmware stalls caused by EMI-induced code jumps in motor cabinets. Industrial -40 C to +85 C operation meets IEC 60068-2-1/2 environmental stress requirements for factory-floor deployment. The 20-SSOP footprint supports reflow soldering on standard FR-4 PCBAs used in industrial DIN-rail modules.
Recommended
Hobby and Educational Development
The PIC16C621AT-20I/SS remains popular in university microcontroller courses and hobbyist projects where students learn assembly programming on the original PIC16C architecture. The PIC16C621A instruction set of only 35 single-word instructions keeps the learning curve manageable, and the ICSP interface on RB6/RB7 allows programming with low-cost tools such as the PICkit 2 or PICkit 3. The 20-SSOP package adapts easily to breadboard-friendly breakout boards used in academic labs. Although obsolete for new commercial designs, the device is still stocked in small quantities for educational kits and labs with established curricula. Migrating to PIC16F628-I/SS gives students the same architecture with the bonus of in-circuit reprogrammability.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C621AT-20I/SS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C621A-20E/SS | PIC16C620AT-20/SS | PIC16C620A-20I/SS | PIC16F628-I/SS |
|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 20-SSOP | 20-SSOP - same | 20-SSOP - same | 20-SSOP - same | 20-SSOP - same |
| Program Memory Type | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 3.5 KB Flash (upgrade) |
| Max Clock Frequency | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz |
| Data RAM | 96 bytes | 96 bytes | 96 bytes | 96 bytes | 224 bytes (upgrade) |
| Analog Comparators | 2 | 2 | 1 | 1 | 2 |
| I/O Pins | 13 | 13 | 13 | 13 | 16 |
| Operating Temperature | -40 C to +85 C (Industrial) | -40 C to +125 C (Extended) | 0 C to +70 C (Commercial) | -40 C to +85 C (Industrial) | -40 C to +85 C (Industrial) |
Key Differentiators
- Industrial temperature grade in tape-and-reel packaging (vs PIC16C621A-20E/SS)
- Dual on-chip analog comparators vs single comparator on PIC16C620A (vs PIC16C620A-20I/SS)
- OTP deterministic final-code with ICSP field programming (vs PIC16F628-I/SS)
Design Notes
PIC16C621AT-20I/SS uses one-time-programmable EPROM, so firmware must be fully validated before programming. There is no field reprogramming capability; any firmware change requires a new part. For prototype-to-production flexibility, qualify the flash-based PIC16F628-I/SS in parallel - same 20-SSOP footprint, identical pinout, but supports in-circuit reprogramming via ICSP.
Place a 100 nF decoupling capacitor as close as possible to the Vdd pin (pin 14) and a bulk 10 uF tantalum or ceramic capacitor near the Vss pin (pin 5). Keep the oscillator traces short and surround them with a ground pour to minimize EMI pickup. MCLR requires a 10 kohm pull-up to Vdd and a 100 nF capacitor to ground for proper reset; omit the capacitor only in cost-critical designs where reset timing tolerance is wide.
PIC16C621AT-20I/SS SLEEP mode reduces I_dd to a few microamps, suitable for battery-powered applications. Configure the Watchdog Timer postscaler to a long interval (e.g., 256 ms or 1 s) to minimize average current while still recovering from firmware stalls. If using ICSP programming, ensure the ICSP connector does not share pins with loads that exceed 25 mA source/sink, as the in-circuit programmer may not be able to drive those pins reliably during programming.
When using the on-chip analog comparators for sensor thresholding, add a 100 nF bypass cap on the CVREF output pin and keep analog traces away from RB6/RB7 (ICSP) and the oscillator pins to avoid digital switching noise coupling into the comparator inputs. For noisy environments, add a small RC filter (1 kohm + 100 nF) at each analog input to suppress high-frequency noise. The two on-chip comparators share an internal voltage reference; if both comparators need different thresholds, an external resistor divider is required.
Compliance Information
RoHS and REACH compliance per Microchip product page. The PIC16C62x family is not AEC-Q100 qualified; for automotive applications use the PIC16F628-I/SS or AEC-Q100-qualified PIC16F variants.
