ATmega128(L)
Special Function IO
Register – SFIOR
Bit
7
6
–
5
–
4
–
3
ACME
R/W
0
2
1
0
TSM
R/W
0
PUD
R/W
0
PSR0
R/W
0
PSR321
R/W
0
SFIOR
Read/Write
Initial Value
R
0
R
0
R
0
• Bit 2 – PUD: Pull-up disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con-
figuring the Pin” on page 67 for more details about this feature.
Alternate Functions of The Port A has an alternate function as the address low byte and data lines for the External
Port A
Memory Interface.
Table 27. Port A Pins Alternate Functions
Port Pin
PA7
Alternate Function
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)
PA6
PA5
PA4
PA3
PA2
PA1
PA0
Table 28 and Table 29 relates the alternate functions of Port A to the overriding signals shown in
Figure 33 on page 71.
Table 28. Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name
PUOE
PUOV
PA7/AD7
PA6/AD6
PA5/AD5
PA4/AD4
SRE
SRE
SRE
SRE
~(WR | ADA(1)) •
PORTA7 • PUD
~(WR | ADA) •
PORTA6 • PUD
~(WR | ADA) •
PORTA5 • PUD
~(WR | ADA) •
PORTA4 • PUD
DDOE
DDOV
PVOE
PVOV
SRE
SRE
SRE
SRE
WR | ADA
SRE
WR | ADA
SRE
WR | ADA
SRE
WR | ADA
SRE
A7 • ADA | D7
OUTPUT • WR
A6 • ADA | D6
OUTPUT • WR
A5 • ADA | D5
OUTPUT • WR
A4 • ADA | D4
OUTPUT • WR
DIEOE
DIEOV
DI
0
0
0
0
0
0
0
0
D7 INPUT
–
D6 INPUT
–
D5 INPUT
–
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 26 for details.
73
2467P–AVR–08/07
ATMEL [ ATMEL ]
