5

ATmega64(L)

2490LS–AVR–10/06

ATmega103 Compatibility

Mode

By programming the M103C Fuse, the ATmega64 will be compatible with the

ATmega103 regards to RAM, I/O pins and Interrupt Vectors as described above. How-

ever, some new features in ATmega64 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.

Pin Descriptions

VCC

Digital supply voltage.

GND

Ground.

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 ATmega64 as listed

on page 74.

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.

Port B also serves the functions of various special features of the ATmega64 as listed

on page 75.