HYB25D256[16/40/80]0C[E/C/F/T](L)
256 Mbit Double-Data-Rate SDRAM
Functional Description
3.2.3
Read Latency
The Read latency, or CAS latency, is the delay, in clock cycles, between the registration of a Read command and
the availability of the first burst of output data. The latency can be programmed 2, 2.5 and 3 clocks. CAS latency
of 1.5 is supported for DDR200 components only.
If a Read command is registered at clock edge n, and the latency is
m
clocks, the data is available nominally
coincident with clock edge
n + m
(see
Figure 6).
Reserved states should not be used as unknown operation or incompatibility with future versions may result.
3.2.4
Operating Mode
The normal operating mode is selected by issuing a Mode Register Set Command with bits A7-A12 set to zero,
and bits A0-A6 set to the desired values. A DLL reset is initiated by issuing a Mode Register Set command with
bits A7 and A9-A12 each set to zero, bit A8 set to one, and bits A0-A6 set to the desired values. A Mode Register
Set command issued to reset the DLL should always be followed by a Mode Register Set command to select
normal operating mode.
All other combinations of values for A7-A12 are reserved for future use and/or test modes. Test modes and
reserved states should not be used as unknown operation or incompatibility with future versions may result.
CAS Latency = 2, BL = 4
CK
CK
Command
Read
NOP
CL=2
DQS
DQ
NOP
NOP
NOP
NOP
CAS Latency = 2.5, BL = 4
CK
CK
Command
Read
NOP
CL=2.5
DQS
DQ
NOP
NOP
NOP
NOP
Shown with nominal t
AC
, t
DQSCK
, and t
DQSQ
.
Don鈥檛 Care
Figure 6
Required CAS Latencies
Data Sheet
25
Rev. 1.6, 2004-12