TMPR4938 datasheet(255/716 Pages) TOSHIBA

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Chapter 9 SDRAM Controller

9-21

Bit

Mnemonic

Field Name

Description

Read/Write

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

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

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

CASL

CAS Latency

CAS Latency (tCASL) (Default: 1)

Specifies the CAS latency.

0: 2 tCK

1: 3 tCK

R/W

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

Active Command

Delay

Delay Activate (tDA) (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 tCK

1: 1 tCK

R/W

SWB

Slow Write Burst

Slow Write Burst (tSWB) (Default: 1)

Specifies whether to perform Slow Write Burst.

0: Burst Write occurs at each 1 tCK

1: Burst Write occurs at each 2 tCK

R/W

13:12

—

Reserved

⎯

11:0

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

µs@100 MHz in this

situation.

R/W

Figure 9.4.2 SDRAM Timing Register (2/2)

1 tCK = Clock cycle

2 tRC is used during (i) refresh cycle time, (ii) single Read, (iii) two transfer burst Reads. The bank cycle time is tRAS +

tRP + 1tCK if tRAS + tRP < tRC in the case of (ii) (iii).

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