73
2467S–AVR–07/09
ATmega128
Special Function IO
Register – 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 “Con-
figuring the Pin” on page 67 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 28 and Table 29 relates the alternate functions of Port A to the overriding signals shown in
Figure 33 on page 71.
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.
Bit 7 6 5 4 3 2 1 0
TSM – – – ACME PUD PSR0 PSR321 SFIOR
Read/Write R/W R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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. Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name PA7/AD7 PA6/AD6 PA5/AD5 PA4/AD4
PUOE SRE SRE SRE SRE
PUOV ~(WR
| ADA
(1)
) •
PORTA7 • PUD
~(WR | ADA) •
PORTA6 • PUD
~(WR | ADA) •
PORTA5 • PUD
~(WR | ADA) •
PORTA4 • PUD
DDOE SRE SRE SRE SRE
DDOV WR
| ADA WR | ADA WR | ADA WR | ADA
PVOE SRE SRE SRE SRE
PVOV A7 • ADA | D7
OUTPUT • WR
A6 • ADA | D6
OUTPUT • WR
A5 • ADA | D5
OUTPUT • WR
A4 • ADA | D4
OUTPUT • WR
DIEOE 0 0 0 0
DIEOV 0 0 0 0
DID7 INPUTD6 INPUTD5 INPUTD4 INPUT
AIO – – – –
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