Datasheet

382
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
Figure 31-9. External Memory Timing (SRWn1 = 0, SRWn0 = 0
Table 31-17. External Data Memory Characteristics, 2.7 to 5.5 Volts, SRWn1 = 1, SRWn0 = 0
Symbol Parameter
4MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL
Oscillator Frequency 0.0 8 MHz
10 t
RLDV
Read Low to Data Valid 690 3.0t
CLCL
-60
ns
12 t
RLRH
RD Pulse Width 735 3.0t
CLCL
-15
15 t
DVWH
Data Valid to WR High 750 3.0t
CLCL
16 t
WLWH
WR Pulse Width 735 3.0t
CLCL
-15
Table 31-18. External Data Memory Characteristics, 2.7 to 5.5 Volts, SRWn1 = 1, SRWn0 = 1
Symbol Parameter
4MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL
Oscillator Frequency 0.0 8 MHz
10 t
RLDV
Read Low to Data Valid 690 3.0t
CLCL
-60
ns
12 t
RLRH
RD Pulse Width 735 3.0t
CLCL
-15
14 t
WHDX
Data Hold After WR High 485 2.0t
CLCL
-15
15 t
DVWH
Data Valid to WR High 750 3.0t
CLCL
16 t
WLWH
WR Pulse Width 735 3.0t
CLCL
-15
ALE
T1 T2 T3
Write
Read
WR
T4
A15:8
AddressPrev. addr.
DA7:0
Address DataPrev. data XX
RD
DA7:0 (XMBK = 0)
DataAddress
System Clock (CLK
CPU
)
1
4
2
7
6
3a
3b
5
8 12
16
13
10
11
14
15
9