Rev0.2, Aug. 2006

CMS3216LAx-75Ex

Note :

13. CKE is HIGH for all commands shown except SELF REFRESH.

14. A0-A10 define the op-code written to the mode register.

15. A0-A10 provide row address, and BS determine which bank is made active.

16. A0-A8 provide column address; A10 HIGH enables the auto precharge feature (non-persistent), while A10 LOW disables the auto precharge feature; BS determine which

bank is being read from or written to.

17. A10 LOW: BS determine the bank being precharged. A10 HIGH: All banks precharged and BS is “Don’t Care.”

18. This command is AUTO REFRESH if CKE is HIGH, SELF REFRESH if CKE is LOW.

19. Internal refresh counter controls row addressing; all inputs and I/Os are “Don’t Care” except for CKE.

20. Activates or deactivates the DQs during WRITEs (zero-clock delay) and READs (two-clock delay).

DQM0 controls DQ 0-7, DQM1 controls DQ 8-15, DQM2 controls DQ 16-23 and DQM3 controls DQ 24-31.

Commands

Table 6. provides a reference of all the commands available

with the state of the control signals for executing a specific

command.

COMMAND INHIBIT

The COMMAND INHIBIT function effectively deselects the

SDRAM by preventing new commands from being executed by

the SDRAM, regardless of whether the CLK signal is enabled.

Operations already in progress are not affected.

LOAD MODE REGISTER

The mode register is loaded via inputs A0-A10, BS. The

LOAD MODE REGISTER and LOAD EXTENDED MODE

REGISTER commands can only be issued when all

banks are idle, and a subsequent executable command cannot

definition for the Mode Register and Extended Mode Register.

NO OPERATION (NOP)

The NO OPERATION (NOP) command is used to perform a

NOP to an SDRAM which is selected (/CS is LOW). This pre-

vents unwanted commands from being registered during idle

or wait states. Operations already in progress are not affected.

ACTIVE

The ACTIVE command is used to activate a row in a particular

bank for a subsequent access. The value on the BS inputs

selects the bank, and the address provided on inputs

A0-A10 selects the row. This row remains active for accesses

until a PRECHARGE command is issued to that bank. A

PRECHARGE command must be issued before opening a

different row in the same bank.

READ

READ command is used to initiate a burst read access to an

active row. The value on the BS inputs selects the bank,

and the address provided on inputs A0-A8 selects the starting

column location. The value on input A10 determines whether or

not auto precharge is used. If auto precharge is selected, the

row being accessed will be precharged at the end of the READ

burst. If auto precharge is not selected, the row will remain

open for subsequent accesses. Read data appears on the DQs

subject to the logic level on the DQM inputs two clocks earlier. If

a given DQM signal was registered HIGH, the corresponding

DQs will be High-Z two clocks later; if the DQM signal was

registered LOW, the DQs will provide valid data.

WRITE

The WRITE command is used to initiate a burst write access

to an active row. The value on the BS inputs selects the

bank, and the address provided on inputs A0-A8 selects the

starting column location. The value on input A10 determines

whether or not auto precharge is used. If auto precharge is

selected, the row being accessed will be precharged at the end

of the WRITE burst. If auto precharge is not selected, the row

will remain open for subsequent accesses. Input data appearing

on the DQs is written to the memory array subject to the DQM

input logic level appearing coincident with the data. If a given

DQM signal is registered LOW, the corresponding data will be

written to memory; if the DQM signal is registered HIGH, the

corresponding data inputs will be ignored, and a WRITE will not

be executed to that byte/column location.

PRECHARGE

The PRECHARGE command is used to deactivate the active

row in a particular bank or the active row in all banks. The

bank(s) will be available for a subsequent row access a spec-

Input A10 determines whether one or all banks are to be pre-

charged, and in the case where only one bank is to be pre-

charged, inputs BS select the bank. Otherwise BS is treated as

“Don’t Care.” Once a bank has been pre-charged, it is in the

idle state and must be activated prior to any READ or WRITE

commands being issued to that bank.

AUTO PRECHARGE

AUTO PRECHARGE is accomplished by using A10 to enable

auto precharge in conjunction with a specific READ or WRITE

command. AUTO PRECHARGE thus performs the same

PRECHARGE command described above , without requiring an

explicit command. A PRECHARGE of the bank/row that is

addressed with the READ or WRITE command is automatically

performed upon completion of the READ or WRITE burst.

AUTO PRECHARGE does not apply in the full page mode burst.

Auto precharge is nonpersistent in that it is either enabled or

disabled for each individual READ or WRITE command.

Auto precharge ensures that the precharge is initiated at the

earliest valid stage within a burst. The user must not issue

another command to the same bank until the precharge time

BURST TERMINATE

The BURST TERMINATE command is used to truncate either

fixed-length or full-page bursts. The most recently registered

READ or WRITE command prior to the BURST TERMINATE

command will be truncated.