ATMEGA640 Datasheet, PDF (378/407 Pages) ATMEL Corporation – 8- BIT Microcontroller with 256K Bytes In-System Programmable Flash

Table 173. External Data Memory Characteristics, 2.7 - 5.5 Volts, No Wait-state (Continued)
4 MHz Oscillator
Variable Oscillator
Symbol Parameter
Min
Max
Min
Max
12 t_RLRH
RD Pulse Width
235
13 t_DVWL
Data Setup to WR Low
105
1.0t_CLCL-15
0.5t_CLCL-20⁽¹⁾
14 t_WHDX
Data Hold After WR High
235
1.0t_CLCL-15
15 t_DVWH
Data Valid to WR High
250
1.0t_CLCL
16 t_WLWH
WR Pulse Width
235
1.0t_CLCL-15
Notes: 1. This assumes 50% clock duty cycle. The half period is actually the high time of the external clock, XTAL1.
2. This assumes 50% clock duty cycle. The half period is actually the low time of the external clock, XTAL1.
Table 174. External Data Memory Characteristics, 2.7 - 5.5 Volts, SRWn1 = 0, SRWn0 = 1
4 MHz Oscillator
Variable Oscillator
Symbol Parameter
Min
Max
Min
Max
0 1/t_CLCL
10 t_RLDV
12 t_RLRH
15 t_DVWH
16 t_WLWH
Oscillator Frequency
Read Low to Data Valid
RD Pulse Width
Data Valid to WR High
WR Pulse Width
0.0
8
440
2.0t_CLCL-60
485
2.0t_CLCL-15
500
2.0t_CLCL
485
2.0t_CLCL-15
Unit
ns
ns
ns
ns
ns
Unit
MHz
ns
ns
ns
ns
Table 175. External Data Memory Characteristics, 2.7 - 5.5 Volts, SRWn1 = 1, SRWn0 = 0
4 MHz Oscillator
Variable Oscillator
Symbol Parameter
Min
Max
Min
Max
0 1/t_CLCL
10 t_RLDV
12 t_RLRH
15 t_DVWH
16 t_WLWH
Oscillator Frequency
Read Low to Data Valid
RD Pulse Width
Data Valid to WR High
WR Pulse Width
0.0
8
690
3.0t_CLCL-60
735
3.0t_CLCL-15
750
3.0t_CLCL
735
3.0t_CLCL-15
Unit
MHz
ns
ns
ns
ns
Table 176. External Data Memory Characteristics, 2.7 - 5.5 Volts, SRWn1 = 1, SRWn0 = 1
4 MHz Oscillator
Variable Oscillator
Symbol Parameter
Min
Max
Min
Max
0 1/t_CLCL
Oscillator Frequency
0.0
8
10 t_RLDV
Read Low to Data Valid
690
3.0t_CLCL-60
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
Unit
MHz
ns
ns
ns
ns
ns
378 ATmega640/1280/1281/2560/2561
2549A–AVR–03/05