ATMEGA64A-AU Memory and Peripheral Guide: 64 KB Flash, 4 KB SRAM, 2 KB EEPROM and Serial Interfaces

Memory at a Glance: 64 KB Flash, 4 KB SRAM, 2 KB EEPROM and External Memory Space

The ATMEGA64A-AU is an AVR 8-bit microcontroller from Microchip Technology Inc. with three separate on-chip memory blocks, each serving a different purpose in a design. The Flash program memory is 64 KB and is in-system self-programmable. Internal SRAM is 4 KB. EEPROM is 2 KB.

For an OEM/ODM engineer sizing a design, these three numbers answer three different questions. Flash holds the application code, so 64 KB is the ceiling for the firmware image, including any bootloader or self-programming routine that runs from the same array. SRAM holds stack, buffers and run-time variables, so 4 KB determines how much working data can exist at once. EEPROM holds parameters that must survive a power cycle without being rewritten by the application firmware, so 2 KB is the budget for calibration values, counters and configuration records.

The device also provides an optional external memory space of 64 KB. That figure matters at the architectural level: if the internal memory budget is not the right fit, the design has a documented external memory option to consider rather than requiring a different part on the board.

Flash Endurance and Data Retention: What the Numbers Mean for Fielded Equipment

The published endurance figures for this device are 10000 write/erase cycles for Flash and 100000 write/erase cycles for EEPROM. Data retention is stated as 20 years at 85 °C and 100 years at 25 °C.

For EMS teams and design owners, the split between those two sets of numbers drives where data is stored. Firmware in the 64 KB Flash array is reprogrammed comparatively rarely, so the Flash cycle count is normally considered against production reflashing and field firmware updates rather than against routine operation. The 2 KB EEPROM, with the higher cycle count, is the block intended for values that the application rewrites during the life of the product.

The retention figures are equally practical, because they are quoted at two temperatures. Equipment that operates in a warm enclosure is judged against the 85 °C figure, while equipment that spends its life at ordinary room temperature is judged against the 25 °C figure. Both figures are stated by the manufacturer as retention ratings for the device; they are not projections made by NexCir.

Design teams should also note that the EEPROM endurance and retention numbers apply to the EEPROM array specifically, and the Flash numbers to the Flash array. The two are separate specifications and should be tracked separately in a design review.

Serial Interfaces: Dual USART, SPI and Two-Wire Serial Interface

The ATMEGA64A-AU carries three distinct serial blocks, and the count of each is what determines whether a system topology can be implemented without external bridging.

There are two USART interfaces, described as dual programmable serial USARTs. Two independent asynchronous serial ports are what allow a product to hold a host link and a second serial link at the same time. The SPI interface is capable of Master/Slave operation, which means the same device can act as the bus controller toward a peripheral or as a subordinate to another controller. The Two-wire Serial Interface is present as a single, byte-oriented block and is I2C-compatible.

For a purchasing manager reading a bill of materials, the value of this table is that it fixes the number of external interface circuits that may be required. Two USARTs, one SPI and one two-wire bus are what the part provides; a design that needs more of any one of them has to be architected differently.

Timers, PWM and Real-Time Functions

Timing resources are usually the first peripherals to run short in a control application, so the counts matter as much as the memory figures.

The device provides two 16-bit Timer/Counters with compare and capture modes, and two 8-bit Timer/Counters. Capture mode is relevant where an input event must be timestamped in hardware; compare mode is relevant where an output must toggle at a defined count. Six PWM channels with programmable resolution from 1 to 16 bits are available, plus two dedicated 8-bit PWM channels.

Two further blocks handle timekeeping independently of the main timing chain. The Real Time Counter has its own separate oscillator, and the programmable watchdog timer has a separate on-chip oscillator as well. Because both use separate oscillators, they are not tied to the timer/counter clock chain, which is what makes them usable for periodic wake-up and for recovery from a stalled program.

Analog Front End: 10-bit ADC Channels and Analog Comparator

The analog-to-digital converter is a 10-bit successive approximation type with 8 channels. Of those, 8 are single-ended channels, and 2 differential channels are available with programmable gain of 1x, 10x or 200x.

The gain options are the significant detail for signal acquisition. A small differential signal can be amplified on-chip at 10x or 200x before conversion, which is a documented device capability that a design can use instead of adding an external amplifier stage. The single-ended channel count sets how many independent signals can be sampled without external multiplexing.

An on-chip analog comparator is also present. Where a design only needs a threshold decision rather than a converted value, the comparator provides that function inside the device, again reducing the external component count.

For engineers deciding whether signal acquisition can remain on-chip, the practical assessment is: count the single-ended signals, count the differential signals that need gain, and check whether a threshold comparison can replace a conversion. The ATMEGA64A-AU documents all three capabilities.

Core, I/O and Integration Features: Registers, Throughput, JTAG, QTouch and ATmega103 Mode

The execution core is an AVR 8-bit architecture with a 130-instruction set, most of which execute in a single clock cycle. At 16 MHz the device delivers 16 MIPS. The speed grade for the industrial and extended order codes is 0 to 16 MHz. There are 32 × 8-bit general purpose working registers.

Register count and instruction throughput together shape how much of the 64 KB Flash budget is consumed by a given algorithm, which is why these figures belong alongside the memory numbers rather than in a separate discussion.

There are 53 programmable I/O lines. The absolute maximum DC current per I/O pin is 40.0 mA, and that is a stress rating rather than a normal operating current — it defines the limit beyond which the pin may be damaged, not a drive specification to design against.

Integration features include an IEEE std. 1149.1 compliant boundary-scan JTAG interface, which supports board-level interconnect verification during production. Capacitive touch support is documented as up to 64 QTouch sense channels, allowing touch keys to be implemented without separate touch controllers. The device also offers an ATmega103 compatibility mode, selectable by a fuse, for designs that need it.

Operating Conditions: Supply Voltage, Temperature Grades and Sleep Modes

The operating voltage range for VCC is 2.7 to 5.5 V. Two temperature grades are documented, and the choice between them is an ordering-code decision.

Industrial order codes -AU and -MU are rated for an operating temperature range (TA) of -40 to +85 °C. Extended order codes -AN and -MN are rated for -40 to +105 °C. Both grades share the 0 to 16 MHz speed grade.

Six sleep modes are available: Idle, ADC Noise Reduction, Power-save, Power-down, Standby and Extended Standby. The number of modes matters because each one switches off a different combination of clocks and peripherals; a design that must wake periodically has different requirements from one that must sleep until an external event.

Two absolute maximum figures are published for the device and must be read as stress ratings only:

The distinction between the two blocks of that table is the one most often blurred in procurement documents. The 6.0 V and -55 to +125 °C figures describe the limits the part can survive, not the conditions under which it is specified to operate. Ordering to a temperature grade is the correct way to specify an operating environment.

Package Options and Ordering Codes

The ordering code ATMEGA64A-AU designates a 64-lead TQFP in package type 64A. The body measures 14 x 14 mm with 1.0 mm thickness and a 0.8 mm lead pitch. The pin count is 64.

The same die is also offered in a second package: a 64-pad QFN/MLF, package type 64M1, with a 9 x 9 x 1.0 mm body and a 0.50 mm lead pitch. For layout engineers the difference is straightforward — the QFN/MLF occupies a smaller board footprint with a finer pitch, while the TQFP uses a leaded package with a wider pitch.

Tape and reel order codes are ATmega64A-AUR, -ANR, -MUR and -MNR, covering the package and temperature combinations in reel form. Packaging compliance is stated as Pb-free, RoHS compliant, Halide free and fully Green. The device is also available in wafer form through the manufacturer's sales office.

How to Request a Quote

NexCir can prepare a quotation for the ATMEGA64A-AU against a defined requirement. To make the request unambiguous, include the order code you need — noting whether the design requires the 64-lead TQFP or the 64-pad QFN/MLF — the temperature grade, whether tape and reel is required, and the quantity. If the requirement involves the extended temperature grade or a specific reel code, state it explicitly so the quotation matches the order code rather than the base part number.

Send those details to NexCir and a quotation will be prepared against them.

Related reading

• How Can You Secure Original ATMEGA32A-AU and ATMEGA64A-AU with Fresh Date Codes?

References

1. ATmega64A Datasheet Complete, Atmel-8160E (09/2015)