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:

Table 45. Port G Pins Alternate Functions

• 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 input of the inverting 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 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.

• 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.

• WR – Port G, Bit 0

WR is the external data memory write control strobe.

Table 46 and Table 47 relates the alternate functions of Port G to the overriding signals shown in Figure 33 on page 68.

Table 46. Overriding Signals for Alternate Functions in PG4..PG1

82 ATmega128

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ATmega128

Table 47. Overriding Signals for Alternate Functions in PG0

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