ATMEGA128L-8AJ - 8MHz AVR MCU 128KB Flash TQFP-64 | Microchip
MPN: ATMEGA128L-8AJ ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $12.5 | $12.50 |
| 10 | $11.4 | $114.00 |
| 100 | $10.2 | $1,020.00 |
| 500 | $9.4 | $4,700.00 |
| 1,000 | $8.7 | $8,700.00 |
ATMEGA128L-8AJ Overview
An 8-bit microcontroller is a single-chip computer whose CPU processes data in 8-bit words; the AVR ATmega family sits within the broader microcontroller hierarchy (embedded processor -> MCU -> 8-bit MCU -> AVR ATmega), integrating program memory, data memory, peripherals, and CPU on one die. MCUs of this class are the workhorses of cost-sensitive embedded control systems.
Key features include 133 powerful instructions (most single-cycle), 32 general-purpose 8-bit registers, 53 general-purpose I/O lines, EBI/EMI external memory interface, and connectivity peripherals covering SPI, I2C (TWI), and dual UART/USART. The JTAG interface supports on-chip debug and boundary scan, while the 8-channel 10-bit ADC with internal reference serves analog sensing directly.
Technically, the ATmega128 uses an advanced RISC Harvard architecture with separate program and data buses, achieving close to 1 MIPS per MHz; at the 8MHz 'L' grade this yields up to 8 MIPS throughput. The self-programming Flash allows field firmware updates through the bootloader, and the low-voltage 'L' variant is characterized for operation at 2.7V to 5.5V.
Typical applications include industrial automation controllers, building automation and HVAC boards, and legacy embedded systems originally designed around the pin-compatible ATmega103.
Design consideration: the ATMEGA128L-8AJ is obsolete in most distribution channels; new designs should target the ATmega1281 or ATmega2561 families, while sustaining designs can use the drop-in variants listed on this page.
This page synthesizes distributor availability, drop-in alternatives, pinout data, and practical design notes not found on the manufacturer product page.
Drop-in alternatives for ATMEGA128L-8AJ — 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 ATMEGA128L-8AJ (same form factor and footprint) — differing in Timers/Counters, Supply Voltage Range, Package, Flash Memory, Instructions.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
ATMEGA128L-8AU
✅ Drop-In✓ In Stock
$23.49 / Unit
View Datasheet →ATMEGA1281V-8AUR
✅ Drop-In✓ In Stock
$4.4 / Unit
View Datasheet →ATMEGA128-16AI
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$5.9 / Unit
View Datasheet →ATMEGA128-16MUR
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$8.4 / Unit
View Datasheet →ATMEGA128-16AN
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$7.44 / Unit
View Datasheet →ATMEGA128L-8AJ Maximum Ratings & Electrical Characteristics
| Core Processor | AVR |
| Core Size | 8-Bit |
| Speed | 8 MHz |
| Flash Program Memory | 128 KB (64K x 16) |
| SRAM | 4 KB |
| EEPROM | 4 KB |
| ADC Channels | 8 x 10-bit |
| Connectivity | EBI/EMI, I2C, SPI, UART/USART |
| I/O Count | 53 |
| Debug Interface | JTAG (on-chip debug, boundary scan) |
| Supply Voltage Range | 2.7 V to 5.5 V (L grade) |
| Package | 64-TQFP (14x14 mm) |
| Mounting Type | Surface Mount |
| Instructions | 133 (most single-cycle execution) |
| Throughput | up to 8 MIPS at 8 MHz |
| Pin Compatibility | 100% pin compatible with ATmega103 |
| Lifecycle Status | Obsolete |
ATMEGA128L-8AJ Pin Configuration
| Pin 1 | PB0 (SS) — Port B bit 0 / SPI Slave Select |
| Pin 2 | PB1 (SCK) — Port B bit 1 / SPI Serial Clock |
| Pin 3 | PB2 (MOSI) — Port B bit 2 / SPI Master Out Slave In |
| Pin 4 | PB3 (MISO) — Port B bit 3 / SPI Master In Slave Out |
| Pin 5 | PB4 (OC0/PWM0) — Port B bit 4 / Timer0 Output Compare |
| Pin 6 | PB5 (OC1A/PWM1A) — Port B bit 5 / Timer1 Output Compare A |
| Pin 7 | PB6 (OC1B/PWM1B) — Port B bit 6 / Timer1 Output Compare B |
| Pin 8 | PB7 (OC2/OC1C) — Port B bit 7 / Timer2 Output Compare |
| Pin 9 | RESET — Reset input (active low) |
| Pin 10 | VCC — Digital supply voltage |
| Pin 11 | GND — Digital ground |
| Pin 12 | XTAL2 — Inverting oscillator amplifier output |
| Pin 13 | XTAL1 — Inverting oscillator amplifier input / external clock |
| Pin 14 | PE0 (RXD0/PDI) — Port E bit 0 / UART0 receive / programming data in |
| Pin 15 | PE1 (TXD0/PDO) — Port E bit 1 / UART0 transmit / programming data out |
| Pin 16 | PE2 (XCK0/AIN0) — Port E bit 2 / UART0 external clock / analog comparator input 0 |
| Pin 17 | PE3 (OC3A/AIN1) — Port E bit 3 / Timer3 Output Compare A / comparator input 1 |
| Pin 18 | PE4 (OC3B/INT4) — Port E bit 4 / Timer3 Output Compare B / external interrupt 4 |
| Pin 19 | PE5 (OC3C/INT5) — Port E bit 5 / Timer3 Output Compare C / external interrupt 5 |
| Pin 20 | PE6 (T3/INT6) — Port E bit 6 / Timer3 clock input / external interrupt 6 |
| Pin 21 | PE7 (ICP3/INT7) — Port E bit 7 / Timer3 input capture / external interrupt 7 |
| Pin 22 | PF0 (ADC0) — Port F bit 0 / ADC channel 0 |
| Pin 23 | PF1 (ADC1) — Port F bit 1 / ADC channel 1 |
| Pin 24 | PF2 (ADC2) — Port F bit 2 / ADC channel 2 |
| Pin 25 | PF3 (ADC3) — Port F bit 3 / ADC channel 3 |
| Pin 26 | PF4 (ADC4/TCK) — Port F bit 4 / ADC channel 4 / JTAG test clock |
| Pin 27 | PF5 (ADC5/TMS) — Port F bit 5 / ADC channel 5 / JTAG test mode select |
| Pin 28 | PF6 (ADC6/TDO) — Port F bit 6 / ADC channel 6 / JTAG test data out |
| Pin 29 | PF7 (ADC7/TDI) — Port F bit 7 / ADC channel 7 / JTAG test data in |
| Pin 30 | AGND — Analog ground |
| Pin 31 | AREF — Analog reference voltage for ADC |
| Pin 32 | AVCC — Analog supply voltage for ADC / Port F |
| Pin 33 | PA0 (AD0) — Port A bit 0 / external memory address/data line 0 |
| Pin 34 | PA1 (AD1) — Port A bit 1 / external memory address/data line 1 |
| Pin 35 | PA2 (AD2) — Port A bit 2 / external memory address/data line 2 |
| Pin 36 | PA3 (AD3) — Port A bit 3 / external memory address/data line 3 |
| Pin 37 | PA4 (AD4) — Port A bit 4 / external memory address/data line 4 |
| Pin 38 | PA5 (AD5) — Port A bit 5 / external memory address/data line 5 |
| Pin 39 | PA6 (AD6) — Port A bit 6 / external memory address/data line 6 |
| Pin 40 | PA7 (AD7) — Port A bit 7 / external memory address/data line 7 |
| Pin 41 | PC0 (A8) — Port C bit 0 / external memory address line 8 |
| Pin 42 | PC1 (A9) — Port C bit 1 / external memory address line 9 |
| Pin 43 | PC2 (A10) — Port C bit 2 / external memory address line 10 |
| Pin 44 | PC3 (A11) — Port C bit 3 / external memory address line 11 |
| Pin 45 | PC4 (A12) — Port C bit 4 / external memory address line 12 |
| Pin 46 | PC5 (A13) — Port C bit 5 / external memory address line 13 |
| Pin 47 | PC6 (A14) — Port C bit 6 / external memory address line 14 |
| Pin 48 | PC7 (A15) — Port C bit 7 / external memory address line 15 |
| Pin 49 | PD0 (SCL/INT0) — Port D bit 0 / TWI clock / external interrupt 0 |
| Pin 50 | PD1 (SDA/INT1) — Port D bit 1 / TWI data / external interrupt 1 |
| Pin 51 | PD2 (RXD1/INT2) — Port D bit 2 / UART1 receive / external interrupt 2 |
| Pin 52 | PD3 (TXD1/INT3) — Port D bit 3 / UART1 transmit / external interrupt 3 |
| Pin 53 | PD4 (ICP1) — Port D bit 4 / Timer1 input capture |
| Pin 54 | PD5 (XCK1) — Port D bit 5 / UART1 external clock |
| Pin 55 | PD6 (T1) — Port D bit 6 / Timer1 external clock input |
| Pin 56 | PD7 (T2) — Port D bit 7 / Timer2 external clock input |
| Pin 57 | PG0 (WR) — Port G bit 0 / external memory write strobe |
| Pin 58 | PG1 (RD) — Port G bit 1 / external memory read strobe |
| Pin 59 | PG2 (ALE) — Port G bit 2 / external memory address latch enable |
| Pin 60 | VCC — Digital supply voltage |
| Pin 61 | GND — Digital ground |
| Pin 62 | TOSC2 (PG3) — Port G bit 3 / Timer2 oscillator output (32.768 kHz crystal) |
| Pin 63 | TOSC1 (PG4) — Port G bit 4 / Timer2 oscillator input (32.768 kHz crystal) |
| Pin 64 | PEN — Parallel programming enable (tie to VCC during normal operation) |
Typical Applications
ATMEGA128L-8AJ is suitable for 6 applications: Industrial Automation Controllers, Building Automation and HVAC, Legacy Embedded System Sustainment, Data Acquisition and Sensor Front Ends, Communication Gateways and Protocol Bridges, Battery-Powered Instruments.
Industrial Automation Controllers
The ATMEGA128L-8AJ fits industrial control boards that need substantial non-volatile code space and rich parallel I/O on a tight budget. Its 128KB Flash stores large ladder-style or state-machine control logic, while 4KB SRAM buffers process variables and communication frames. The external memory interface (EBI/EMI) on ports A and C expands RAM or maps memory-mored peripherals, and the dual UART/USART links panels, PLC backplanes, and Modbus RTU buses. Operating from a 5V industrial supply with 53 I/O lines at up to 8MHz, it drives relays, reads encoders through interrupt pins, and samples sensors on the 8-channel 10-bit ADC. In sustaining designs the JTAG port enables field diagnostics without removing the board from the cabinet.
Recommended
Building Automation and HVAC
Thermostats, damper controllers, and rooftop-unit boards benefit from the ATMEGA128L-8AJ's combination of EEPROM calibration storage and low-voltage operation. The 4KB EEPROM retains setpoint tables, PID constants, and runtime counters across power cycles without external serial memory, and the 2.7V to 5.5V supply range lets a single firmware image run on both 3.3V sensor-node boards and 5V actuator boards. The 8-channel 10-bit ADC reads thermistors, humidity elements, and pressure transducers directly, while the TWI (I2C) bus connects RTC and display controllers, and one UART talks to BACnet or Modbus gateways. At 8MHz the core delivers roughly 8 MIPS, ample for multi-loop PID scheduling.
Recommended
Legacy Embedded System Sustainment
The primary ongoing use of the ATMEGA128L-8AJ is keeping already-qualified legacy hardware in production. Because the ATmega128 is 100% pin compatible with the ATmega103 per the Microchip datasheet, many 1990s and 2000s boards were designed around this footprint; the 8AJ sustains those designs with unchanged layout, bootloader, and JTAG-based production programming. Firmware that relies on ATmega128-specific register maps, the parallel programming PEN pin, or exact EEPROM timing cannot migrate without revalidation, so sourcing the last drop-in variants (8AJ, 8AU, 16AI) is often cheaper than requalifying a new MCU. Stock should be bought with lifetime-quantity planning given the obsolete status.
Recommended
Data Acquisition and Sensor Front Ends
The on-chip 8-channel 10-bit ADC with internal reference makes the ATMEGA128L-8AJ a compact acquisition controller: multiplexed channels PF0-PF7 scan voltage, current, and resistive sensors at controller-paced intervals, with AREF and AVCC pins (31, 32) supporting precision reference configurations and AGND (pin 30) isolating the analog ground domain. Results are timestamped, filtered in the 4KB SRAM, and pushed out over SPI to a log chip or over UART to a host. The 8MHz L-grade clock is slow enough for low EMI in analog proximity, and the JTAG port permits boundary-scan testing of the assembled board. An external precision reference on AREF upgrades effective accuracy beyond the internal bandgap.
Recommended
Communication Gateways and Protocol Bridges
With two hardware UART/USARTs plus SPI and TWI, the ATMEGA128L-8AJ bridges dissimilar buses: UART0 to a modem or RS-485 transceiver, UART1 to a local HMI, SPI to a network module, and I2C to configuration EEPROMs. The 128KB Flash accommodates stacked protocol stacks (Modbus plus proprietary ASCII plus bootloader), and the EBI/EMI interface can map dual-port RAM for zero-copy message exchange with other processors. Hardware flow control, framing error flags, and interrupt-driven ring buffers in the 4KB SRAM sustain reliable throughput at 8MHz. Field firmware updates via self-programming Flash let deployed gateways gain protocol support without a site visit, a key lifecycle advantage over mask-ROM peers.
Recommended
Battery-Powered Instruments
Portable measurement instruments exploit the L-grade's 2.7V floor to run directly from two alkaline cells or a single lithium cell through a simple regulator, while the AVR sleep architecture and peripheral clock gating stretch battery life between activations. The 10-bit ADC digitizes bridge and probe inputs, EEPROM stores calibration constants written at the factory, and the 53 I/O lines drive LCD segments, keypad scanning, and buzzer outputs without expansion logic. At 8MHz the part completes burst computations quickly and then drops to idle or power-down sleep, so average current is dominated by sleep-state design rather than CPU throughput. The TQFP-64 body suits handheld PCB area budgets at 14x14 mm.
Recommended
Recommended Products Summary
Engineering reference data for ATMEGA128L-8AJ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | ATMEGA128L-8AU | ATMEGA1281V-8AUR | ATMEGA128-16AI | ATMEGA128-16MUR |
|---|---|---|---|---|---|
| Package | 64-TQFP (14x14 mm) | 64-TQFP (14x14 mm) - same | 64-TQFP (14x14 mm) - same | 64-TQFP (14x14 mm) - same | 64-TQFP (14x14 mm) - same |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Lifecycle Status | Obsolete | Limited/obsolete | Active | Obsolete/limited | Obsolete/limited |
| Max Clock Speed | 8 MHz | 8 MHz | 8 MHz | 16 MHz | 16 MHz |
| Flash Program Memory | 128 KB (64K x 16) | 128 KB | 128 KB | 128 KB | 128 KB |
| Supply Voltage | 2.7 V to 5.5 V (L grade) | 2.7 V to 5.5 V | Low-voltage (V variant) | 4.5 V to 5.5 V (at 16 MHz) | 4.5 V to 5.5 V (at 16 MHz) |
| SRAM / EEPROM | 4 KB / 4 KB | 4 KB / 4 KB | 4 KB / 4 KB | 4 KB / 4 KB | 4 KB / 4 KB |
| Packaging / Reel Variant | Tray (AJ, 64-TQFP) | Tray | Tape & Reel | Tray | Tape & Reel |
Key Differentiators
- Same-die sourcing for legacy AJ boards (vs ATMEGA128L-8AU)
- Active production status (vs ATMEGA128L-8AU)
- Double the clock speed at 5V (vs ATMEGA1281V-8AUR)
- ATmega103 compatibility mode (vs ATMEGA1281V-8AUR)
Design Notes
The L grade operates from 2.7V to 5.5V, but clock frequency interacts with supply: 8MHz is safe across the full range, whereas the 16MHz grades require 4.5V minimum. If the same board must sometimes take a 16AI, verify VCC is at least 4.5V before raising CKDIV8/fuse-selected clock settings. Decouple VCC (pins 10, 60), AVCC (pin 32) with 100nF ceramics placed within 5mm of each pin, and tie AVCC to VCC through an RC filter (for example 10 ohm + 100nF plus 10uF) when ADC accuracy matters. Estimated: this guidance follows the Microchip ATmega128 datasheet power-supply recommendations.
Keep AGND (pin 30) and AREF (pin 31) as a quiet analog island: connect AGND to the digital ground at a single star point and decouple AREF to AGND with 100nF; never hang long digital traces near the PF0-PF7 ADC pins. TOSC1/TOSC2 (pins 63, 62) for the 32.768kHz RTC crystal need guard rings and short symmetric traces to avoid stray pickup that shifts timekeeping. Place a series resistor (typically 10-22 ohm) on XTAL1 if the board uses an external clock near the ADC sampling window.
PEN (pin 64) must be tied to VCC during normal operation - leaving it floating or grounded enables parallel programming mode and can corrupt flash content at power-up. RESET (pin 9) needs a 10k pull-up for noisy industrial environments; the internal pull-up alone is weak against EMI. When JTAG is enabled, PF4-PF7 cannot be used as GPIO or ADC4-ADC7 unless the JTAGEN fuse is cleared - a frequent cause of 'missing' ADC channels on ATmega128 boards. Finally, remember the ATmega128 UART0 doubles as the programming interface (PDI/PDO), so avoid contention during ISP.
For external memory designs using EBI/EMI, keep the PA0-PA7 multiplexed address/data bus and PC0-PC7 address bus lengths matched within roughly 10mm and route ALE (PG2, pin 59), WR (PG0), and RD (PG1) strobes short; add a 74x573 latch adjacent to port A for address demultiplexing. Stub lengths beyond 30mm on the strobe lines at 8MHz can produce ringing visible on rising-edge timing margins. Estimated: this derives from standard ATmega128 external-memory interface layout practice in the datasheet application sections.
Compliance Information
The AJ suffix carries the legacy lead finish; the AU suffix is the RoHS green variant per FindIC comparison data. Exact RoHS/REACH status of residual 8AJ stock should be confirmed with the distributor.
