Datasheet

Datasheet 113

Bit Description

27:26 Back To Back Read-Write commands spacing (DDR, same or different

Rows/Bank): This field determines the RD-WR command spacing, in terms of common

clocks based on the following formula: CL + 0.5xBL + TA (RD-WR) – DQSS

DQSS: is time from Write command to data and is always 1 CK

BL: is Burst Length which is set to 4 or 8.

TA (RD-WR): is required DQ turn-around, can be set to 1, 2 or 3 CK

CL: is CAS latency, can be set to 2 or 2.5

Examples of usage:

For BL=4, with single DQ turn-around and CL=2, this field must be set to 4 CK (2+2+1-1)

For BL=8, with single DQ turn-around and CL=2.5, this field must be set to 8 CK

(2.5+4+2-1)

Encoding CK between RD and WR commands

BL = 4 BL=8

00: 7 9

01: 6 8

10: 5 7

11: 4 6

NOTE: Since reads in DDR SDRAM cannot be terminated by Writes, the Space

between commands is not a function of Cycle Length but of Burst Length.

25 Back To Back Read-Read commands spacing (DDR, different Rows):

This field determines the RD-RD Command Spacing, in terms of common clocks based

on the following formula: 0.5xBL + TA(RD-RD)

BL: is Burst Length and can be set to 4 or 8.

TA (RD-RD): is required DQ turn-around, can be set to 1 or 2 CK

Examples of usage:

For BL=4, with single DQ turn-around, this field must be set to 3 CK (2+1)

For BL=8, with single DQ turn-around, this field must be set to 6 CK (4+2)

Encoding CK between RD and RD commands

BL = 4 BL = 8

0: 4 6 for 2 TA (Read-Read)

1: 3 5 for 1 TA (Read-Read)

NOTE: Since a Read to a different row does not terminate a Read, the Space between

commands is not a function of Cycle Length but of Burst Length.

24:15 Reserved