Page 111 - Digital Electronics by harish

4.5 SDRAM

Synchronous Dynamic Random Access Memory (SDRAM) is a faster memory than
ordinary Dynamic RAM (DRAM). SDRAM is mainly used in computers. Ordinary DRAM
operates in an asynchronous manner. They react to changes as the control inputs change, and
also they are only able to operate as the requests are presented to them, dealing with one at a
time. SDRAM is able to operate more efficiently. It is synchronized to the clock of the
processor.

With SDRAM having a synchronous interface, it has an internal finite state machine
(FSM) that pipelines incoming instructions. This enables the SDRAM to operate in a more
complex fashion than an asynchronous DRAM. This enables it to operate at much higher
speeds. As a result of this, SDRAM is capable of keeping two sets of memory addresses open
simultaneously. By transferring data alternately from one set of addresses, and then the other,
SDRAM reduces the delays associated with asynchronous DRAM.

SDRAM Pins

A0 – A11 Address Inputs

DQ0 – DQ15 Data Inputs / Outputs
RAS Row Address Strobe Input

CAS Column Address Strobe Input

CLK Clock Input

CKE Clock Enable Input

WE Write Enable Input
BA0 & BA1 Bank Selection Inputs

DQM Data Mask Input

Figure : Pins of a typical SDRAM Chip

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