Figure 9-4. External Data Memory Cycles with SRWn1 = 0 and SRWn0 = 1(1)
T1
T2
T3
T4
T5
System Clock (CLKCPU
)
ALE
A15:8 Prev. addr.
DA7:0 Prev. data
WR
Address
Data
Address
Address
XX
DA7:0 (XMBK = 0) Prev. data
DA7:0 (XMBK = 1) Prev. data
RD
Data
Data
Address
Note:
1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T5 is only present if the next instruction accesses the RAM (internal
or external).
Figure 1. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 0(1)
T1
T2
T3
T4
T5
T6
System Clock (CLKCPU
)
ALE
A15:8 Prev. addr.
DA7:0 Prev. data
WR
Address
Data
Address
Address
XX
DA7:0 (XMBK = 0) Prev. data
DA7:0 (XMBK = 1) Prev. data
RD
Data
Data
Address
Note:
1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T6 is only present if the next instruction accesses the RAM (internal
or external).
30
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
