MSC8144E Reference Manual, Rev. 3
12-12
Freescale
Semiconductor
DDR SDRAM Memory Controller
12.3
DDR SDRAM Clocking and Interface Timing
The DDR memory controller supports four-beat bursts to SDRAM. For single-beat reads, the
DDR memory controller performs a four-beat burst read but ignores the last three beats.
Single-beat writes are performed by masking the last three beats of the four-beat burst using the
data mask
MDM[0–3]
. If ECC is disabled, writes smaller than words are performed by
appropriately activating the data mask. If ECC is enabled, the controller performs a read-modify
write.
Note:
If a second read or write is pending, reads shorter than four beats are not terminated
early even if some data is irrelevant.
To accommodate available memory technologies across a wide spectrum of operating
frequencies, the DDR memory controller allows you to set the timing intervals listed in Table
12-8 with a granularity of one memory clock cycle, except for the CASLAT field, which can be
programmed with a 1/2 clock granularity.
The value of these parameters (in whole clock cycles) must be set by application software at
system initialization before the DDR controller is enabled and must be kept in the DDR memory
controller configuration registers. Any update of the timing parameters should be done while the
controller is disabled.
Table 12-8. DDR SDRAM Interface Timing Intervals
Timing Intervals
Definition
Register/Page
ACTTOACT
The number of clock cycles from a bank-activate command to
another bank-activate command within a physical bank. This
interval is listed in the AC specifications of the SDRAM as
t
RRD.
DDR SDRAM Timing Configuration
Register 1 (TIMING_CFG_1)
page 12-38
ACTTOPRE
Activate-to-Precharge Interval
The number of clock cycles from an activate command until a
precharge command is allowed. This interval is listed in the
AC specifications of the SDRAM as t
RAS
.
ACTTORW
Activate-to-Read/Write Interval for SDRAM
The number of clock cycles from an activate command until a
read or write command is allowed. This interval is listed in the
AC specifications of the SDRAM as t
RCD
.
BSTOPRE
Open Page Interval
The number of clock cycles to maintain a page open after an
access. The page open duration counter is reloaded with
BSTOPRE each time the page is accessed (including page
hits). When the counter expires, the open page is closed with
a SDRAM precharge bank command as soon as possible.
DDR SDRAM Interval Configuration
Register
page 12-49
CASLAT
MCAS Latency from READ Command
Used in conjunction with additive latency to obtain the READ
latency. The number of clock cycles between the registration
of a READ command by the SDRAM and the availability of the
first piece of output data. If a READ command is registered at
clock edge
n
, and the read latency is
m
clocks, the data is
available nominally coincident with clock edge
n
+
m
.
DDR SDRAM Timing Configuration
Register 1 (TIMING_CFG_1)
page 12-38
Summary of Contents for MSC8144E
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Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...