M65KG256AB datasheet(23/51 Pages) STMICROELECTRONICS

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M65KG256AB

5 Registers description

23/51

Registers description

The DDR Mobile RAM has the two mode registers, the Mode Register and the Extended Mode

5.1

Mode Register description

The Mode Register is used to select the CAS Latency, Burst Type, and Burst Length of the

device:

●

The CAS Latency defines the number of clock cycles after which the first data will be

output during a Burst Read operation.

●

The Burst Type specifies the order in which the burst data will be addressed. This order is

programmable either to sequential or interleaved (see Table 5: Burst Type Definition).

●

The Burst Length is the number of Words that will be output or input during a Burst Read

or Write operation. It can be configured as 2, 4, 8 or 16 Words.

The Mode Register must be programmed at the end of the Power-Up sequence prior to issuing

any command. It is loaded by issuing a Mode Register Set command (MRS), with BA0-BA1 are

set to ‘00’ to select the Mode Register.

Table 7: Mode Register Definition, shows the available Mode Register configurations.

Table 7.

Mode Register Definition

Address

Bits

Mode

Value

Description

A12-A7

000000

A6-A4

MR6-MR4

CAS Latency Bits

(Read Operations)

011

3 Clock Cycles

Other configurations reserved

MR3

Burst Type Bit

Sequential

Interleaved

A2-A0

MR2-MR0

Burst Length Bit

001

2 Words

010

4 Words

011

8 Words

100

16 Words

Other configurations reserved

BA1-BA0

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