ATmega64A datasheet(5/392 Pages) ATMEL

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8160C–AVR–07/09

ATmega64A

2.2.1

ATmega103 Compatibility Mode

By programming the M103C Fuse, the ATmega64A will be compatible with the ATmega103

regards to RAM, I/O pins and Interrupt Vectors as described above. However, some new fea-

tures in ATmega64A are not available in this compatibility mode, these features are listed below:

• One USART instead of two, asynchronous mode only. Only the eight least significant bits of

the Baud Rate Register is available.

• One 16 bits Timer/Counter with two compare registers instead of two 16 bits Timer/Counters

with three compare registers.

• Two-wire serial interface is not supported.

• Port G serves alternate functions only (not a general I/O port).

• Port F serves as digital input only in addition to analog input to the ADC.

• Boot Loader capabilities is not supported.

• It is not possible to adjust the frequency of the internal calibrated RC Oscillator.

• The External Memory Interface can not release any Address pins for general I/O, neither

configure different wait states to different External Memory Address sections.

• Only EXTRF and PORF exist in the MCUCSR Register.

• No timed sequence is required for Watchdog Timeout change.

• Only low-level external interrupts can be used on four of the eight External Interrupt sources.

• Port C is output only.

• USART has no FIFO buffer, so Data OverRun comes earlier.

• The user must have set unused I/O bits to 0 in ATmega103 programs.

2.3

Pin Descriptions

2.3.1

VCC

Digital supply voltage.

2.3.2

GND

Ground.

2.3.3

Port A (PA7:PA0)

Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The

Port A output buffers have symmetrical drive characteristics with both high sink and source

capability. As inputs, Port A pins that are externally pulled low will source current if the pull-up

resistors are activated. The Port A pins are tri-stated when a reset condition becomes active,

even if the clock is not running.

Port A also serves the functions of various special features of the ATmega64A as listed on page

75.

2.3.4

Port B (PB7:PB0)

Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The

Port B output buffers have symmetrical drive characteristics with both high sink and source

capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up

resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,

even if the clock is not running.

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