183
4.17 Bus Timing
[Explanation of operation]
Write control is performed with only the CAS control signals (including CASL an d CASH)
while RAS is lowered to "L", and then WE (includ ing WEL and WEH) is lowered to "L".
Column ad dresses and output data are output in Q4 and Q5 cycles.
CS area (CS4/CS5) switch-over in high-speed page mode, read and write combination,
2CAS/1WE
Figure 4.17-27 Example 3 of DRAM Interface Timing Chart in High-Speed Page Mode
[Explanation of operation]
Even if the CS area is switched, RAS remains at "L" in high-speed page m ode.
When a b us cyc le st ar ts from a hi gh- s pee d p age, RDX in a re ad cycle goes down to "L" from
the rising edge of Q4 and is negated when the Q5 cycle ends. In a write cy cle, it goe s down
to "L" from the rising edge of WE (including WEL and WEH) Q4 and is negated whe n the Q5
cycle ends.
CS4X and CS5 X change at the same time as the output ad dress. When a bus cycle starts
from a high-speed page, they change from the Q4 cycle as wit h the column address.
Q4
CLK
A24-00 CS5X col.adr CS5X col.adr CS5X col.adr CS4X col.adr CS4X col.adr
D31-24 Write
D23-16 Read Write
CS4X
CS5X
RDX
CS4:RAS
CS4:CASL
CS4:CASH
CS4:WE
CS5:RAS
CS5:CASL
CS5:CASH
CS5:WE
CS5 area
Q5 Q4 Q5 Q4 Q5 Q4 Q5 Q4 Q5
CS4 area
Idle
Read Write
Write Read
Read Read
Read