ATMEGA161L-4AC - 16KB Flash 4MHz AVR MCU 44-TQFP | Microchip
MPN: ATMEGA161L-4AC ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $8.5 | $8.50 |
| 10 | $7.85 | $78.50 |
| 100 | $7.15 | $715.00 |
| 500 | $6.65 | $3,325.00 |
| 1,000 | $6.2 | $6,200.00 |
ATMEGA161L-4AC Overview
An 8-bit microcontroller is a complete computing system on a single chip, combining a processor core, program memory, data memory, timers, and serial communication peripherals into one package. Within the embedded hierarchy, the AVR ATmega family sits under Microchip's (formerly Atmel's) microcontroller product line, which itself belongs to the broader categories of MCU, integrated circuit, and semiconductor.
Key features include the Advanced RISC architecture executing 130 powerful instructions, most in a single clock cycle; 32 general-purpose working registers; three flexible Timer/Counters with compare modes; a real-time counter; and a programmable Watchdog Timer with an internal oscillator.
Technically, the ATmega161 integrates two programmable serial UARTs - a distinguishing feature for its class - plus an SPI serial interface and internal and external interrupt sources. The external oscillator type supports precise clocking, and the device supports In-System Programming and Self-programming of Flash for field updates. External memory expansion is supported through an address/data bus interface.
Typical applications include legacy industrial control systems, dual-UART communication gateways, appliance control boards, and maintenance/repair of existing ATmega161-based equipment.
Design consideration: since the ATmega161 family is discontinued, new designs should target its pin-compatible successor ATmega162, while repair programs can fall back on this L-grade 4MHz variant for low-voltage systems.
This page synthesizes distributor availability, drop-in alternatives, pricing history, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for ATMEGA161L-4AC — 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 ATMEGA161L-4AC (same form factor and footprint) — differing in Instruction Set, Mounting Type, Supply Voltage Range, EEPROM Size, Flash Memory.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
ATMEGA161L-4PI
✅ Drop-In✓ In Stock
$6.35 / Unit
View Datasheet →ATMEGA161-4AC
✅ Drop-In ⚠️ 参数待验证📋 Reference alternative (not in catalog)
ATMEGA162-16AU
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$2.45 / Unit
View Datasheet →ATMEGA16-16AU
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$4.41 / Unit
View Datasheet →ATMEGA128-16AU
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$14.3 / Unit
View Datasheet →ATMEGA161L-4AC Maximum Ratings & Electrical Characteristics
| Core Processor | AVR 8-bit |
| Core Size | 8-bit |
| Speed | 4 MHz |
| Program Memory Size | 16 KB (8K x 16) FLASH |
| Program Memory Type | FLASH (In-System or Self-programmable) |
| RAM Size | 1 KB (1K x 8) SRAM |
| EEPROM Size | 512 bytes |
| Number of I/O | 35 |
| Working Registers | 32 general purpose |
| Instruction Set | 130 powerful instructions, most single-cycle |
| Connectivity | SPI, 2x UART/USART |
| Peripherals | 3x Timer/Counter with Compare, WDT, Real-time Counter |
| Oscillator Type | External |
| Package / Case | 44-TQFP (10x10 mm) |
| Mounting Type | Surface Mount |
| Packaging | Tray |
ATMEGA161L-4AC Pin Configuration
| Pin 1 | PB0/SS — Port B bit 0 / SPI Slave Select |
| Pin 2 | PB1/T1 — Port B bit 1 / Timer1 external clock input |
| Pin 3 | PB2/AIN0 — Port B bit 2 / Analog Comparator input 0 |
| Pin 4 | PB3/AIN1 — Port B bit 3 / Analog Comparator input 1 |
| Pin 5 | PB4/OC0 — Port B bit 4 / Timer0 Output Compare |
| Pin 6 | PB5/SCK — Port B bit 5 / SPI Serial Clock |
| Pin 7 | PB6/MISO — Port B bit 6 / SPI Master In Slave Out |
| Pin 8 | PB7/MOSI — Port B bit 7 / SPI Master Out Slave In |
| Pin 9 | RESET — Active-low reset input |
| Pin 10 | VCC — Digital supply voltage |
| Pin 11 | GND — Ground |
| Pin 12 | XTAL1 — External oscillator input |
| Pin 13 | XTAL2 — External oscillator output |
| Pin 14 | PD0/RXD0 — Port D bit 0 / UART0 receive |
| Pin 15 | PD1/TXD0 — Port D bit 1 / UART0 transmit |
| Pin 16 | PD2/RXD1 — Port D bit 2 / UART1 receive |
| Pin 17 | PD3/TXD1 — Port D bit 3 / UART1 transmit |
| Pin 18 | PD4/INT0 — Port D bit 4 / External interrupt 0 |
| Pin 19 | PD5/INT1 — Port D bit 5 / External interrupt 1 |
| Pin 20 | PD6/ICP1 — Port D bit 6 / Timer1 Input Capture |
| Pin 21 | PD7/OC2 — Port D bit 7 / Timer2 Output Compare |
| Pin 22 | PC0 — Port C bit 0 / general purpose I/O |
| Pin 23 | PC1 — Port C bit 1 / general purpose I/O |
| Pin 24 | PC2 — Port C bit 2 / general purpose I/O |
| Pin 25 | PC3 — Port C bit 3 / general purpose I/O |
| Pin 26 | PC4 — Port C bit 4 / general purpose I/O |
| Pin 27 | PC5 — Port C bit 5 / general purpose I/O |
| Pin 28 | PC6 — Port C bit 6 / general purpose I/O |
| Pin 29 | PC7/TOSC2 — Port C bit 7 / RTC oscillator output |
| Pin 30 | PC8/TOSC1 — RTC oscillator input pin (TOSC1) |
| Pin 31 | PA7 — Port A bit 7 / address/data bus (external memory) |
| Pin 32 | PA6 — Port A bit 6 / address/data bus (external memory) |
| Pin 33 | PA5 — Port A bit 5 / address/data bus (external memory) |
| Pin 34 | PA4 — Port A bit 4 / address/data bus (external memory) |
| Pin 35 | PA3 — Port A bit 3 / address/data bus (external memory) |
| Pin 36 | PA2 — Port A bit 2 / address/data bus (external memory) |
| Pin 37 | PA1 — Port A bit 1 / address/data bus (external memory) |
| Pin 38 | PA0 — Port A bit 0 / address/data bus (external memory) |
| Pin 39 | VCC — Digital supply voltage |
| Pin 40 | GND — Ground |
| Pin 41 | PE0/ALE — Port E bit 0 / External memory Address Latch Enable |
| Pin 42 | PE1/OC1B — Port E bit 1 / Timer1 Output Compare B |
| Pin 43 | PE2/OC1A — Port E bit 2 / Timer1 Output Compare A |
| Pin 44 | WR/RD — External memory write/read strobes |
Typical Applications
ATMEGA161L-4AC is suitable for 6 applications: Legacy Industrial Control Systems, Dual-UART Communication Gateways, SPI Peripheral Expansion and Monitoring, Appliance and Consumer Equipment Control, Battery-Powered Low-Voltage Instruments, External-Memory Expandable Data Loggers.
Legacy Industrial Control Systems
The ATMEGA161L-4AC fits legacy industrial control boards originally designed around the ATmega161 because it is the exact silicon that these controllers were qualified with. Its 16KB Flash holds ladder-style or state-machine control firmware, while 1KB SRAM and 512B EEPROM retain setpoints and counters across power cycles. The 35 I/O lines directly drive relays, contactors, and indicator stacks through the three Timer/Counters with compare modes for deterministic PWM and timing. In repair and sustaining programs, swapping a failed device with the identical 4MHz L-grade part avoids any requalification: no firmware changes, no crystal retuning, and identical electrical behavior on 24V industrial panel boards. Supply from broker stock is the trade-off, so maintenance planners should buy spares in batches while stock persists.
Recommended
Dual-UART Communication Gateways
The distinguishing feature of the ATMEGA161L-4AC for protocol conversion work is its pair of programmable serial UARTs, rare in 8-pin-count AVRs of its generation. A gateway can simultaneously listen on an RS-485 field bus on UART0 and stream to an RS-232 service port on UART1, buffering messages in the 1KB SRAM. At 4MHz, the AVR core sustains baud rates up to 38.4 kbps on both ports concurrently with headroom for framing and CRC checks in the 130-instruction single-cycle RISC core. The external oscillator ensures the baud-rate generator accuracy needed for multi-drop buses, and the Watchdog Timer with internal oscillator recovers the link after bus faults. This makes the part well suited to maintaining installed Modbus-RTU style bridges and repeater nodes that cannot be redesigned.
Recommended
SPI Peripheral Expansion and Monitoring
With its hardware SPI interface, the ATMEGA161L-4AC acts as an efficient master for serial EEPROMs, RTCs, ADCs, and display drivers in existing designs. The SPI bus plus the parallel external-memory interface let one low-cost MCU coordinate both fast local peripherals and memory-mapped I/O, using ALE and read/write control lines on the expansion port. The 4MHz external clock gives deterministic SPI SCK rates suitable for legacy data-acquisition cards where cycle-accurate sampling intervals are enforced by Timer/Counter interrupts. Three flexible Timer/Counters with compare modes timestamp events without core intervention, conserving the 1KB SRAM for data staging. In sustaining engineering, this part keeps 1990s-era SPI-based instrument control boards running without any layout or firmware changes.
Recommended
Appliance and Consumer Equipment Control
White-goods and small-appliance controllers from the ATmega161 generation used exactly this L-grade part for its low-voltage tolerance and robust I/O count. The 35 general-purpose I/O lines cover keypads, seven-segment or LCD drive, triac controls, and door-interlock sensing without port expanders, while the 512-byte EEPROM stores cycle counters and user preferences through power interruptions. The programmable Watchdog Timer with its own internal oscillator guarantees recovery from lockups even if the main 4MHz external oscillator fails - an important safety behavior in heater and motor-control appliances. Because the die is unchanged from fielded units, a service replacement restores original firmware behavior, EMC characteristics, and safety qualifications, avoiding the recertification cost that any redesign would trigger.
Recommended
Battery-Powered Low-Voltage Instruments
The 'L' speed grade of the ATMEGA161L-4AC is the low-voltage member of the family, characterized for operation down to approximately 2.7V at 4MHz, which makes it appropriate for 3-cell battery instruments designed to run without a 5V regulator stage. The external oscillator allows a low-cost 4MHz crystal chosen for accurate Timer/Counter timing during measurement windows, while idle and power-down sleep modes stretch battery life between readings. The real-time counter keeps long-interval logs independent of the main clock, and 512 bytes of EEPROM retains calibration constants across battery swaps. For repair of portable gauges, meters, and loggers, specifying the identical L-grade die preserves the validated power budget of the original design.
Recommended
External-Memory Expandable Data Loggers
Unlike many small AVRs, the ATMEGA161L-4AC includes a full external memory expansion interface with address latching (ALE) and read/write strobes, letting designs extend beyond the internal 1KB SRAM using standard SRAM or memory-mapped peripherals. A data logger can thus dedicate internal SRAM as a fast ring buffer while cycling large external SRAM banks for extended event storage, timed by the three compare-mode Timer/Counters. The dual UARTs allow one port for sensor intake and a second for periodic offload to a host, and the Watchdog Timer guarantees logger recovery in unattended installations. For keeping aging logger platforms in service, the identical 44-TQFP device drops onto the existing board with the original 4MHz crystal and bus timing fully preserved.
Recommended
Recommended Products Summary
Engineering reference data for ATMEGA161L-4AC — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | ATMEGA161L-4PI | ATMEGA162-16AU | ATMEGA16-16AU | ATMEGA128-16AU |
|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 44-TQFP (10x10 mm) | 44-TQFP (10x10 mm) - same | 44-TQFP (10x10 mm) - same | 44-TQFP (10x10 mm) - same | 44-TQFP (AVR TQFP family) |
| Max Speed | 4 MHz | 4 MHz | 16 MHz | 16 MHz | 16 MHz |
| Flash | 16 KB | 16 KB | 16 KB | 16 KB | 128 KB |
| SRAM | 1 KB | 1 KB | 1 KB | 1 KB | 4 KB |
| EEPROM | 512 bytes | 512 bytes | 512 bytes | 512 bytes | 4 KB |
| UART / USART Count | 2 | 2 | 2 | 1 | 2 |
| ADC | No | No | No | Yes, 8ch 10-bit | Yes, 8ch 10-bit |
| Lifecycle Status | Obsolete | Obsolete (broker stock only) | Active | Active | Active |
Key Differentiators
- Dual UARTs in a 16KB AVR (vs ATMEGA16-16AU)
- True ATmega161 silicon for legacy repair (vs ATMEGA162-16AU)
- External memory expansion interface (vs ATMEGA16-16AU)
Design Notes
The ATMEGA161L-4AC is an obsolete part sourced from broker inventory, so date codes and plating may vary between batches. Before committing to a production repair run, verify the package suffix (C = commercial grade, lead finish may be legacy tin-lead on older stock) against your RoHS obligations, and request date-code photos. The 'L' grade is rated at 4MHz only; do not substitute a higher-speed clock expecting full characterization, as the low-voltage speed limit is the binding constraint on this die.
The 44-TQFP (10x10 mm) footprint requires the 0.8mm pitch land pattern per the Atmel package drawing; keep the crystal within 15mm of XTAL1/XTAL2 with short return grounds, since the 4MHz external oscillator drives both UART baud-rate generators and any timing error shifts both serial ports simultaneously. Decouple both VCC pins (10 and 39) individually with 100nF ceramics placed within 5mm of each pin, and provide a solid ground plane for the SPI bus integrity.
Estimated: the L-grade ATmega161 is characterized for operation down to approximately 2.7V at 4MHz per the family datasheet. When powering from a 3V battery rail, budget for active current in the low single-digit mA range at 4MHz plus peripheral current for two UARTs and SPI. If your board must also accept a 5V supply during programming, check the ISP programmer voltage compatibility - programming a 3V system with a 5V-only ISP tool risks overstressing the die.
Compliance Information
Compliance status not stated in reviewed distributor listings. Commercial-grade ('C' suffix) legacy part may have tin-lead plating depending on date code; the industrial 4PI variant carries Pb-free plating per suffix coding. Request material declarations from the seller.
