ATmega128
Special Function IO
Register – SFIOR
Bit
7
TSM
Read/Write
Initial Value
R/W
0
6
–
R
0
5
–
R
0
4
–
R
0
3
ACME
R/W
0
2
PUD
R/W
0
1
PSR0
R/W
0
0
PSR321
R/W
0
SFIOR
• 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
for more details about this feature.
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 27.
Port A Pins Alternate Functions
Port Pin
PA7
PA6
PA5
PA4
PA3
PA2
PA1
PA0
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)
and
relates the alternate functions of Port A to the overriding signals shown in
Table 28.
Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name
PUOE
PUOV
DDOE
DDOV
PVOE
PVOV
DIEOE
DIEOV
DI
AIO
Note:
PA7/AD7
SRE
~(WR | ADA
) •
PORTA7 • PUD
SRE
WR | ADA
SRE
A7 • ADA | D7
OUTPUT • WR
0
0
D7 INPUT
–
PA6/AD6
SRE
~(WR | ADA) •
PORTA6 • PUD
SRE
WR | ADA
SRE
A6 • ADA | D6
OUTPUT • WR
0
0
D6 INPUT
–
PA5/AD5
SRE
~(WR | ADA) •
PORTA5 • PUD
SRE
WR | ADA
SRE
A5 • ADA | D5
OUTPUT • WR
0
0
D5 INPUT
–
PA4/AD4
SRE
~(WR | ADA) •
PORTA4 • PUD
SRE
WR | ADA
SRE
A4 • ADA | D4
OUTPUT • WR
0
0
D4 INPUT
–
1. ADA is short for ADdress Active and represents the time when address is output. See
for details.
73
2467S–AVR–07/09
ATMEL [ ATMEL CORPORATION ]
