eorex
EM428M1644RTA
Mode Register Definition
Mode Register Set
The mode register stores the data for controlling the various operating modes of DDR SDRAM which
contains addressing mode, burst length, /CAS latency, test mode, DLL reset and various vendor’s specific
opinions. The defaults values of the register is not defined, so the mode register must be written after EMRS
setting for proper DDR SDRAM operation. The mode register is written by asserting low on /CS, /RAS, /CAS,
/WE and BA0 ( The DDR SDRAM should be in all bank precharge with CKE already high prior to writing into
the mode register. ) The state of the address pins A0-A12 in the same cycle as /CS, /RAS, /CAS, /WE and
BA0 going low is written in the mode register. Two clock cycles are requested to complete the write operation
in the mode register. The mode register contents can be changed using the same command and clock cycle
requirements during operating as long as all banks are in the idle state. The mode register is divided into
various fields depending on functionality. The burst length uses A0-A2, addressing mode uses A3, /CAS
latency ( read latency from column address ) uses A4-A6. A7 is used for test mode. A8 is used for DDR reset.
A7 must be set to low for normal MRS operation.
Apr. 2007
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