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9.1. Mode Register Set(MRS)
The mode register is designed to support the various operating modes of Mobile DDR SDRAM. It includes Cas latency, addressing mode,
burst length, test mode and vendor specific options to make Mobile DDR SDRAM useful for variety of applications. The default value of the
mode register is not defined, therefore the mode register must be written in the power up sequence of Mobile DDR SDRAM. The mode register is written by asserting low on CS, RAS, CAS and WE(The Mobile DDR SDRAM should be in active mode with CKE already high prior to
writing into the mode register). The states of address pins A0 ~ A12 and  BA0, BA1 in the same cycle as CS, RAS, CAS and WE going low are
written in the mode register. Two clock cycles are required to complete the write operation in the mode register. Even if the power-up
sequence is finished and some read or write operation is executed afterward, the mode register contents can be changed with the same command and two clock cycles. This command must be issued only when all banks are in the idle state. If mode register is changed, extended
mode register automatically is reset and come into default state. So extended mode register must be set again. 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 ~ A12 is used for test mode. BA0 and BA1 must be set to low for proper MRS operation. 

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