13.3.1
Alternate Functions of Port A
The Port A has an alternate function as the address low byte and data lines for the External
Memory Interface.
Table 13-3. Port A Pins Alternate Functions
Port Pin
Alternate Function
PA7
PA6
PA5
PA4
PA3
PA2
PA1
PA0
AD7 (External memory interface address and data bit 7)
AD6 (External memory interface address and data bit 6)
AD5 (External memory interface address and data bit 5)
AD4 (External memory interface address and data bit 4)
AD3 (External memory interface address and data bit 3)
AD2 (External memory interface address and data bit 2)
AD1 (External memory interface address and data bit 1)
AD0 (External memory interface address and data bit 0)
Table 13-4 and Table 13-5 relates the alternate functions of Port A to the overriding signals
shown in Figure 13-5 on page 76.
Table 13-4. Overriding Signals for Alternate Functions in PA7:PA4
Signal
Name
PA7/AD7
PA6/AD6
PA5/AD5
PA4/AD4
PUOE
SRE
SRE
SRE
SRE
~(WR | ADA(1)) •
PORTA7 • PUD
~(WR | ADA) •
PORTA6 • PUD
~(WR | ADA) •
PORTA5 • PUD
~(WR | ADA) •
PORTA4 • PUD
PUOV
DDOE
DDOV
PVOE
SRE
WR | ADA
SRE
SRE
WR | ADA
SRE
SRE
WR | ADA
SRE
SRE
WR | ADA
SRE
A7 • ADA | D7
OUTPUT • WR
A6 • ADA | D6
OUTPUT • WR
A5 • ADA | D5
OUTPUT • WR
A4 • ADA | D4
OUTPUT • WR
PVOV
DIEOE
DIEOV
DI
0
0
0
0
0
D7 INPUT
–
0
D6 INPUT
–
0
D5 INPUT
–
0
D4 INPUT
–
AIO
Note:
1. ADA is short for ADdress Active and represents the time when address is output. See “Exter-
nal Memory Interface” on page 27 for details.
78
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
