ATmega64A datasheet(87/392 Pages) ATMEL

87 / 392 page

8160C–AVR–07/09

ATmega64A

13.3.7

Alternate Functions of Port G

In ATmega103 compatibility mode, only the alternate functions are the defaults for Port G, and

Port G cannot be used as General Digital Port Pins. The alternate pin configuration is as follows:

• TOSC1 – Port G, Bit 4

TOSC2, Timer Oscillator pin 1: When the AS0 bit in ASSR is set (one) to enable asynchronous

clocking of Timer/Counter0, pin PG4 is disconnected from the port, and becomes the inverting

output of the Oscillator amplifier. In this mode, a crystal Oscillator is connected to this pin, and

the pin can not be used as an I/O pin.

• TOSC2 – Port G, Bit 3

TOSC2, Timer Oscillator pin 2: When the AS0 bit in ASSR is set (one) to enable asynchronous

clocking of Timer/Counter0, pin PG3 is disconnected from the port, and becomes the input of the

inverting Oscillator amplifier. In this mode, a crystal Oscillator is connected to this pin, and the

pin cannot be used as an I/O pin.

• ALE – Port G, Bit 2

ALE is the external data memory Address Latch Enable signal.

•RD – Port G, Bit 1

RD is the external data memory read control strobe.

Table 13-20. Overriding Signals for Alternate Functions in PF3:PF0

Signal

Name

PF3/ADC3

PF2/ADC2

PF1/ADC1

PF0/ADC0

PUOE

000

PUOV

000

DDOE

DDOV

PVOE

000

PVOV

000

DIEOE

000

DIEOV

000

–––

–

AIO

ADC3 INPUT

ADC2 INPUT

ADC1 INPUT

ADC0 INPUT

Table 13-21. Port G Pins Alternate Functions

Port Pin

Alternate Function

PG4

TOSC1 (RTC Oscillator Timer/Counter0)

PG3

TOSC2 (RTC Oscillator Timer/Counter0)

PG2

ALE (Address Latch Enable to external memory)

PG1

RD (Read strobe to external memory)

PG0

WR (Write strobe to external memory)

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