135
ATmega161(L)
1228B–09/01
Figure 86.
External Memory Timing (SRWn1 = 1, SRWn0 = 0)
Figure 87.
External Memory Timing (SRWn1 = 1, SRWn0 = 1)
Note:
1. The ALE pulse in the last period (T4 - T7) is only present if the next instruction
accesses the RAM (internal or external). The data and address will only change in T4
- T7 if ALE is present (the next instruction accesses the RAM).
ALE
WR
RD
Address [15..8]
Address
XX
XX
Read
Data/Address [7..0]
Address
Data
XX
Wr
ite
Data/Address [7..0]
Address
Data
XX
T1
T2
T3
T6
1
4
2
7
6
3a
3b
5
8
12
16
13
15
9
10
11
14
Prev. addr.
XX
Prev. data
XX
Prev. data
System Clock Ø
T4
T5
ALE
WR
RD
Address [15..8]
Address
XX
XX
Read
Data/Address [7..0]
Address
Data
XX
Wr
ite
Data/Address [7..0]
Address
Data
XX
T1
T2
T3
T7
1
4
2
7
6
3a
3b
5
8
12
16
13
15
9
10
11
14
Prev. addr.
XX
Prev. data
XX
Prev. data
T4
T5
T6
System Clock Ø