DDR Sdrams a Suncam Online Continuing Education Course
Memories in Computers—Part 2: DDR SDRAMs A SunCam online continuing education course Memories in Computers Part 2: DDR SDRAMs by Dr. William R. Huber, P.E. www.SunCam.com Copyright 2011 William R. Huber (updated 2018) Page 1 of 43 Memories in Computers—Part 2: DDR SDRAMs A SunCam online continuing education course A. Introduction To understand the operation and advantages of Double Data Rate (DDR) Synchronous Dynamic Random Access Memories (DDR SDRAMs), we will start by reviewing the architecture of a single data rate (SDR) SDRAM. In keeping with industry practice, the balance of this course will refer to SDR SDRAMs simply as SDRAMs. A Micron data sheet provides a functional block diagram.1 1 Micron MT48LC128M4A2 512Mb SDRAM Data Sheet, Rev. M 6/10 EN, page 8 www.SunCam.com Copyright 2011 William R. Huber (updated 2018) Page 2 of 43 Memories in Computers—Part 2: DDR SDRAMs A SunCam online continuing education course SDRAM architecture is very similar to that of an asynchronous DRAM, with the addition of Command Inputs (CS#, WE#, CAS# and RAS#)2, Clock Inputs (CKE, CLK) and Control Logic including Command Decode and Mode Register. Some of the significant differences in the operation of an SDRAM as compared to a DRAM are as follows: • SDRAM operation is initiated by the low to high transition of the external clock, and data bits are input or output in synchronism with the external clock; • In an SDRAM, the operational mode (ACTIVE, READ, WRITE, REFRESH, etc.) is established by a command issued at the beginning of the cycle; • The SDRAM command is defined by the logic state of several inputs (e.g.; RAS#, CAS#, WE# and A10) when CS# (Chip Select) is low, CKE (Clock Enable) is high, and CLK (external Clock) transitions from low to high; • The SDRAM is organized into banks, which can operate virtually independently of each other.
[Show full text]