ATmega128(L)
Alternate Functions of In ATmega103 compatibility mode, only the alternate functions are the defaults for Port G, and
Port G
Port G cannot be used as General Digital Port Pins. The alternate pin configuration is as follows:
Table 45. Port G Pins Alternate Functions
Port Pin
PG4
Alternate Function
TOSC1 (RTC Oscillator Timer/Counter0)
TOSC2 (RTC Oscillator Timer/Counter0)
ALE (Address Latch Enable to external memory)
RD (Read strobe to external memory)
WR (Write strobe to external memory)
PG3
PG2
PG1
PG0
• TOSC1 – Port G, Bit 4
TOSC1, 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 71.
Table 46. Overriding Signals for Alternate Functions in PG4..PG1
Signal Name
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
DIEOE
DIEOV
DI
PG4/TOSC1
PG3/TOSC2
PG2/ALE
PG1/RD
AS0
AS0
SRE
0
SRE
0
0
0
AS0
AS0
SRE
1
SRE
1
0
0
0
0
SRE
ALE
0
SRE
RD
0
0
0
AS0
AS0
0
0
0
0
–
–
–
–
AIO
T/C0 OSC INPUT
T/C0 OSC OUTPUT
–
–
85
2467P–AVR–08/07
ATMEL [ ATMEL ]
