ATmega64(L)
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:
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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.
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Pin Descriptions
VCC
GND
Port A (PA7..PA0)
Digital supply voltage.
Ground.
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.
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2490LS–AVR–10/06
ATMEL [ ATMEL CORPORATION ]
