Toshiba TX49 TMPR4937, Manual

Page: 237 / 553

Chapter 9 SDRAM Controller
9-21
Bit Mnemonic Field Name Description Read/Write
24 ACE Advanced CKE Advanced CKE enable (Default: 0)
Enabling this function makes the timing at which CKE changes one cycle
earlier.
0: Disable
1: Enable R/W
23 PDAE Power Down
Auto Entry Power Down Auto Entry Enable (Default: 0)
Enabling this function makes CKE become “L” while the SDRAMC is in the
Idle state. When refresh, memory access, or command execution is
performed, CKE automatically becomes “H”, the requested operation is
performed, then CKE returns to “L” when the operation is complete.
0: Disable
1: Enable R/W
22:18 RC Refresh Counter Refresh Counter (Default: 000000)
This counter is decremented at each refresh. If the refresh circuit is
activated and a value other than “0” is loaded, this field becomes a down
counter that stops at “0”. A value other than “0” must be reloaded to start
the countdown again. This is used during memory initialization. R/W
17 CASL CAS Latency CAS Latency (t
CASL
) (Default: 1)
Specifies the CAS latency.
0: 2 t
CK
1: 3 t
CK
R/W
16 DRB Data Read
Bypass Data Read Bypass (Default: 0)
Selects the Data Read path used.
0: Data Read latches to the register using the feedback clock.
1: Data Read bypasses the feedback clock latch. R/W
15 DA Active Command
Delay Delay Activate (t
DA
) (Default: 1)
Specifies the delay from the row address to the bank active command.
Setting this bit to “1” sets up the row address two cycles before the active
command is executed.
0: 0 t
CK
1: 1 t
CK
R/W
14 SWB Slow Write Burst Slow Write Burst (t
SWB
) (Default: 1)
Specifies whether to perform Slow Write Burst.
0: Burst Write occurs at each 1 t
CK
1: Burst Write occurs at each 2 t
CK
R/W
13:12 — — Reserved
⎯
11:0 RP Refresh Period Refresh Period (Default: 0x30c)
Specifies the clock cycle count that generates the refresh cycle. Refresh is
only enabled when at least one SDRAM channel is enabled. Please
program the Timing Register before an arbitrary channel is enabled.
Default is 0x30C. A refresh cycle occurs for each 7.8
µ
s@100 MHz in this
situation.
R/W
Figure 9.4.2 SDRAM Timing Register (2/2)
1
t
CK
= Clock cycle
2
t
RC
is used during (i) refresh cycle time, (ii) single Read, (iii) two transfer burst Reads. The bank cycle time is t
RAS
+
t
RP
+ 1t
CK
if t
RAS
+ t
RP
< t
RC
in the case of (ii) (iii).