ATMEGA644P-20PQ - 8-bit AVR MCU 20MHz 64KB Flash DIP-40 | Microchip
MPN: ATMEGA644P-20PQ ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $9.85 | $9.85 |
| 10 | $9.1 | $91.00 |
| 100 | $8.45 | $845.00 |
| 500 | $7.95 | $3,975.00 |
| 1,000 | $7.4 | $7,400.00 |
ATMEGA644P-20PQ Overview
An 8-bit AVR microcontroller is a Harvard-architecture RISC processor that executes most instructions in a single clock cycle, achieving throughputs close to 1 MIPS per MHz. Within the power management and embedded control hierarchy, the ATmega family sits in the mid-range segment between the small ATmega48/328 devices and the larger ATmega1284/2560 parts, making it a common choice for self-contained embedded systems that need substantial Flash without moving to 32-bit architectures.
Key features include the AVR enhanced RISC architecture with 131 powerful instructions, two on-chip UARTs (the P suffix denotes the dual-UART variant with a second USART), an internal RC oscillator, 32 general-purpose I/O lines, and JTAG for on-chip debugging and boundary scan. The device operates from 2.7V to 5.5V, with 20MHz operation specified at 4.5V to 5.5V, and it supports In-System Programming (ISP) as well as self-programming via a boot loader section.
The picoPower CMOS process gives the family flexible power management: idle, power-down, power-save, standby, and extended standby sleep modes allow the system designer to trade processing speed directly against power consumption, a capability Atmel documented as achieving close to 1 MIPS per MHz throughput efficiency.
Typical applications include industrial control panels, test fixtures and instrumentation where the 40-pin DIP package simplifies prototyping and socketed replacement, educational and hobby platforms, and legacy system maintenance where through-hole technology is required.
A key design consideration: Microchip lists this mature device as not recommended for new designs and replaced by ATmega644PA, so new products should target the PA variant, while this part remains useful for maintaining existing socketed designs.
This page synthesizes verified distributor data, drop-in alternatives, and practical design notes not found in the manufacturer datasheet, with pricing references as of 2026-09-18.
Drop-in alternatives for ATMEGA644P-20PQ — 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 ATMEGA644P-20PQ (same form factor and footprint) — differing in Core Architecture, EEPROM, SRAM, Supply Voltage Range, Package.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
ATMEGA1284-PU
✅ Drop-In✓ In Stock
$6.21 / Unit
View Datasheet →ATMEGA1284P-PU
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$6.05 / Unit
View Datasheet →ATMEGA644PA-PU
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$5.15 / Unit
View Datasheet →ATMEGA644P-20PU
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$8.55 / Unit
View Datasheet →ATMEGA644-20PU
✅ Drop-In ⚠️ 参数待验证📋 Reference alternative (not in catalog)
ATMEGA644P-20PQ Maximum Ratings & Electrical Characteristics
| Core Architecture | AVR 8-bit RISC |
| Maximum Clock Frequency | 20 MHz |
| Flash Memory | 64 KB (32K x 16) |
| SRAM | 4 KB (4K x 8) |
| EEPROM | 2 KB |
| Supply Voltage Range | 2.7 V to 5.5 V |
| Operating Voltage (20MHz) | 4.5 V to 5.5 V |
| Number of I/O | 32 |
| Package | 40-PDIP |
| Oscillator Type | Internal RC |
| USARTs | 2 |
| Instruction Set | 131 instructions, mostly single-cycle |
| Processing Throughput | Up to 20 MIPS at 20 MHz (approx. 1 MIPS per MHz) |
| Temperature Range | Extended temperature (industrial) |
| Programming Features | In-System Programmable Flash, self-programming boot section, JTAG |
| Power Modes | Idle, Power-down, Power-save, Standby, Extended Standby (picoPower) |
| Mounting Type | Through Hole |
| RoHS Status | Green (per FindIC listing) |
ATMEGA644P-20PQ Pin Configuration
| Pin 1 | VCC — Digital supply voltage |
| Pin 2 | PA7 (ADC7) — Port A bit 7 / ADC channel 7 |
| Pin 3 | PA6 (ADC6) — Port A bit 6 / ADC channel 6 |
| Pin 4 | PA5 (ADC5) — Port A bit 5 / ADC channel 5 |
| Pin 5 | PA4 (ADC4) — Port A bit 4 / ADC channel 4 |
| Pin 6 | PA3 (ADC3) — Port A bit 3 / ADC channel 3 |
| Pin 7 | PA2 (ADC2) — Port A bit 2 / ADC channel 2 |
| Pin 8 | PA1 (ADC1) — Port A bit 1 / ADC channel 1 |
| Pin 9 | PA0 (ADC0) — Port A bit 0 / ADC channel 0 |
| Pin 10 | GND — Ground |
| Pin 11 | PB7 (OC2A/OC1C) — Port B bit 7 / PWM outputs |
| Pin 12 | PB6 (OC1B) — Port B bit 6 / PWM output |
| Pin 13 | PB5 (OC1A) — Port B bit 5 / PWM output |
| Pin 14 | PB4 (OC0/SS) — Port B bit 4 / Timer0 PWM / SPI slave select |
| Pin 15 | PB3 (MOSI) — Port B bit 3 / SPI master out |
| Pin 16 | PB2 (MISO) — Port B bit 2 / SPI master in |
| Pin 17 | PB1 (SCK) — Port B bit 1 / SPI clock |
| Pin 18 | PB0 (XCK0) — Port B bit 0 / USART0 external clock |
| Pin 19 | PD7 — Port D bit 7 |
| Pin 20 | PD6 — Port D bit 6 |
| Pin 21 | PD5 — Port D bit 5 |
| Pin 22 | PD4 — Port D bit 4 |
| Pin 23 | PD3 — Port D bit 3 |
| Pin 24 | PD2 (RXD1) — Port D bit 2 / USART1 receive |
| Pin 25 | PD1 (TXD1) — Port D bit 1 / USART1 transmit |
| Pin 26 | PD0 (XCK1) — Port D bit 0 / USART1 external clock |
| Pin 27 | PC7 (TCK) — Port C bit 7 / JTAG test clock |
| Pin 28 | PC6 (TMS) — Port C bit 6 / JTAG test mode select |
| Pin 29 | PC5 (TDO) — Port C bit 5 / JTAG test data out |
| Pin 30 | PC4 (TDI) — Port C bit 4 / JTAG test data in |
| Pin 31 | PC3 (TOSC2) — Port C bit 3 / Timer oscillator output |
| Pin 32 | PC2 (TOSC1) — Port C bit 2 / Timer oscillator input |
| Pin 33 | PC1 (SDA) — Port C bit 1 / TWI data |
| Pin 34 | PC0 (SCL) — Port C bit 0 / TWI clock |
| Pin 35 | GND — Ground |
| Pin 36 | AREF — ADC analog reference |
| Pin 37 | AVCC — ADC supply voltage |
| Pin 38 | XTAL1 — Crystal / external clock input |
| Pin 39 | XTAL2 — Crystal output |
| Pin 40 | RESET — Active-low reset input |
Typical Applications
ATMEGA644P-20PQ is suitable for 6 applications: Industrial Control Panels, Test Fixtures and Bench Instrumentation, Educational and Hobby Embedded Platforms, Legacy System Maintenance and EOL Remediation, Serial Communication Gateways, Sensor Data Loggers.
Industrial Control Panels
The ATMEGA644P-20PQ fits industrial control panels that need moderate compute with extended-temperature reliability. Its 64KB Flash accommodates protocol stacks and HMI logic, while the extended-temperature Green PDIP grade supports environments spanning below 0C to above 70C. The 32 I/O lines drive relays, LEDs and button matrices directly, and the dual USARTs (on the P variant) allow simultaneous Modbus RTU communication and debug logging. The 2.7V to 5.5V supply range tolerates noisy 5V industrial rails, and 20MHz at 5V delivers roughly 20 MIPS, sufficient for PID loops at kilohertz rates. Socketed DIP-40 mounting enables fast field replacement of controllers without soldering, reducing downtime in maintenance-intensive facilities.
Recommended
Test Fixtures and Bench Instrumentation
Bench-top test fixtures benefit from the ATMEGA644P-20PQ's through-hole 40-PDIP package, which allows engineers to swap controllers between fixture variants without rework. The JTAG interface enables on-chip debugging and boundary scan during fixture commissioning, while ISP programming supports firmware updates through a simple 2x3 header. With 4KB SRAM and 64KB Flash, the device buffers measurement sequences and stores lookup tables, and the 2KB EEPROM keeps calibration constants through power cycles. The internal RC oscillator allows clock-independent boot, and the dual USARTs can talk to a PC console and the device-under-test simultaneously at 20MHz operation on a 5V supply.
Recommended
Educational and Hobby Embedded Platforms
University labs and maker platforms favor the ATMEGA644P-20PQ because the DIP-40 package survives repeated insertion into sockets and teaches through-hole soldering skills. The AVR architecture, with 131 mostly single-cycle instructions and near 1 MIPS per MHz throughput, is widely documented in academic course material, easing curriculum adoption. Students can program via ISP or a boot loader in the self-programming Flash section, and the peripheral set - timers, ADC, two UARTs, SPI, I2C/TWI - covers a complete embedded systems syllabus. The 20MHz speed grade delivers responsive classroom demos, and the extended-temperature part adds tolerance to unconditioned lab power supplies running at the 5V rail.
Recommended
Legacy System Maintenance and EOL Remediation
Maintaining legacy AVR-based equipment is a primary use case for ATMEGA644P-20PQ, since the part is explicitly positioned as a mature product not recommended for new designs. Procurement teams keep it on hand for socketed replacements in controllers where re-spinning the PCB is uneconomical. Where supply tightens, the pin-compatible ATMEGA1284-PU (active status, 128KB Flash, 8KB SRAM) or the officially recommended ATMEGA644PA provide drop-in paths that reuse the same DIP-40 footprint and connector wiring. Firmware requires only a recompile and register-map review, and the dual USART and 20MHz timing behavior carry over, keeping validation effort minimal for end-of-life remediation programs.
Recommended
Serial Communication Gateways
The dual USARTs of the P-variant make ATMEGA644P-20PQ a natural serial gateway between two asynchronous links, for example bridging a Modbus RTU field bus to a service console. Each USART supports standard baud rates derived from the 20MHz clock with low error percentages, and interrupt-driven ring buffers fit comfortably in the 4KB SRAM. The 64KB Flash leaves headroom for protocol translation, CRC handling and command dispatch. Operation at 5V matches legacy industrial serial transceivers directly, and the DIP-40 package suits low-volume gateway builds where hand assembly and socketed controllers simplify variant configuration. Sleep modes allow duty-cycled gateways to conserve power between polling windows.
Recommended
Sensor Data Loggers
Standalone data loggers exploit the ATMEGA644P-20PQ's 2KB EEPROM for wear-leveling parameter storage and its 10-bit ADC channels on Ports A for sensor inputs. The picoPower sleep architecture - idle, power-down, power-save and standby modes - lets the MCU sleep between sampling intervals, drawing microamp-level current in deep sleep, with an RTC or watchdog scheduled wake-up. At 5V and 20MHz, active-phase processing of sensor data is fast, while the 64KB Flash stores logging firmware plus compression routines. The DIP-40 through-hole package suits hand-built or low-volume logger housings, and the extended-temperature rating keeps the logger reliable in unconditioned outdoor or machinery-adjacent enclosures.
Recommended
Recommended Products Summary
Engineering reference data for ATMEGA644P-20PQ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | ATMEGA1284-PU | ATMEGA1284P-PU | ATMEGA644PA-PU | ATMEGA644P-20PU | ATMEGA644-20PU |
|---|---|---|---|---|---|---|
| Package | 40-PDIP | 40-PDIP - same | 40-PDIP - same | 40-PDIP - same | 40-PDIP - same | 40-PDIP - same |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Flash Memory | 64 KB | 128 KB | 128 KB | 64 KB | 64 KB | 64 KB |
| SRAM | 4 KB | 8 KB | 16 KB | 4 KB | 4 KB | 4 KB |
| Max Clock Speed | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz |
| USART Count | 2 | 2 | 2 | 2 | 2 | 1 |
| Temperature Grade | Extended (industrial) | Commercial 0C to 70C | Commercial 0C to 70C | Commercial 0C to 70C | Commercial 0C to 70C | Commercial 0C to 70C |
| Lifecycle Status | Mature, not recommended for new designs (replaced by ATmega644PA) | Active | Active | Active (recommended successor) | Mature (same family) | Mature (same family) |
Key Differentiators
- Dual USART in the 64KB ATmega class (vs ATMEGA644-20PU)
- Extended-temperature qualification (vs ATMEGA644P-20PU)
- Through-hole 64KB-class availability (vs ATMEGA1284-PU)
Design Notes
Supply design: the ATMEGA644P-20PQ tolerates 2.7V to 5.5V, but 20MHz operation requires 4.5V to 5.5V per the Atmel-42744 datasheet speed-versus-voltage curve. Use a clean 5V rail with 100nF decoupling at each supply pin (VCC pin 1, AVCC pin 37) plus a 10uF bulk capacitor. Tie AVCC to VCC through a low-pass LC filter if ADC accuracy matters, and keep AREF (pin 36) decoupled with 100nF. Brown-out detection should be enabled via fuse settings to prevent Flash corruption during supply dips.
Even though this is a through-hole DIP-40 device, layout discipline still applies. Route the ISP header (MOSI PB3, MISO PB2, SCK PB1, RESET pin 40) as a short, direct 2x3 header near the MCU. Keep the XTAL1/XTAL2 crystal traces (pins 38/39) under 15mm with ground guard traces, and place load capacitors close to the pins. If using JTAG on Port C, reserve the standard 2x5 header footprint so debugging tools connect without ribbon adapters.
Fuse settings are the most common failure source with this device: programming CKOPT/clock fuses incorrectly can leave the chip unresponsive, and disabling RESET (RSTDISBL) permanently bricks in-circuit reprogramming on DIP parts. The JTAG interface is enabled by default and takes over PC4-PC7 - disable via the JTAGEN fuse if those I/O are needed. Finally, since this part is not recommended for new designs, plan the ATMEGA644PA or ATMEGA1284 substitution path early to avoid an emergency redesign when supply ends.
Compliance Information
FindIC and Veswin listings classify the part as Green, indicating lead-free/RoHS-compliant construction. Full REACH and conflict-minerals declarations should be confirmed via Microchip's official compliance portal.
