Special Function Io Register – Sfior - Atmel ATmega128 Manual

Special Function IO
Register – SFIOR
Alternate Functions of
Port A
2467S–AVR–07/09
Bit 7 6
TSM –
Read/Write R/W R
Initial Value 0 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
figuring the Pin" on page 67
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 Alternate Function
PA7 AD7 (External memory interface address and data bit 7)
PA6 AD6 (External memory interface address and data bit 6)
PA5 AD5 (External memory interface address and data bit 5)
PA4 AD4 (External memory interface address and data bit 4)
PA3 AD3 (External memory interface address and data bit 3)
PA2 AD2 (External memory interface address and data bit 2)
PA1 AD1 (External memory interface address and data bit 1)
PA0 AD0 (External memory interface address and data bit 0)
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 PA7/AD7
PUOE SRE
(1)
PUOV ~(WR | ADA ) •
PORTA7 • PUD
DDOE SRE
DDOV WR | ADA
PVOE SRE
PVOV A7 • ADA | D7
OUTPUT • WR
DIEOE 0
DIEOV 0
DI D7 INPUT
AIO –
Note: 1. ADA is short for ADdress Active and represents the time when address is output. See
nal Memory Interface" on page 26
5 4 3
– – ACME
R R R/W
0 0 0
for more details about this feature.
PA6/AD6 PA5/AD5
SRE SRE
~(WR | ADA) • ~(WR | ADA) •
PORTA6 • PUD PORTA5 • PUD
SRE SRE
WR | ADA WR | ADA
SRE SRE
A6 • ADA | D6 A5 • ADA | D5
OUTPUT • WR OUTPUT • WR
0 0
0 0
D6 INPUT D5 INPUT
– –
for details.
ATmega128
2 1 0
PUD PSR0 PSR321
R/W R/W R/W
0 0 0
PA4/AD4
SRE
~(WR | ADA) •
PORTA4 • PUD
SRE
WR | ADA
SRE
A4 • ADA | D4
OUTPUT • WR
0
0
D4 INPUT
–
SFIOR
"Con-
"Exter-
73