ATMEGA128L-8MC View Datasheet(PDF) - Atmel Corporation
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MFG CO.
'ATMEGA128L-8MC' PDF : 395 Pages View PDF
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 configura-
tion is as follows:
Table 45. 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)
• TOSC1 – Port G, Bit 4
TOSC1, Timer Oscillator pin 1: When the AS0 bit in ASSR is set (one) to enable asyn-
chronous 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 asyn-
chronous 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 70.
Table 46. Overriding Signals for Alternate Functions in PG4..PG1
Signal Name PG4/TOSC1
PG3/TOSC2
PG2/ALE
PUOE
AS0
AS0
SRE
PUOV
0
0
0
DDOE
AS0
AS0
SRE
DDOV
0
0
1
PVOE
0
0
SRE
PVOV
0
0
ALE
DIEOE
AS0
AS0
0
DIEOV
0
0
0
DI
–
–
–
AIO
T/C0 OSC INPUT
T/C0 OSC OUTPUT
–
PG1/RD
SRE
0
SRE
1
SRE
RD
0
0
–
–
84 ATmega128
2467O–AVR–10/06
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