What do you mean, DDR2?

Ddr2/ddr II (Double Data Rate 2) SDRAM is a new generation of memory technology standards developed by the JEDEC (Joint Commission on Electronic Equipment Engineering), the biggest difference from the previous generation of DDR memory technology standards, although it was adopted in the rise of the clock/ The basic way of data transfer at the same time, but DDR2 memory has twice times the previous generation of DDR memory pre-read capability (that is, 4bit data read prefetching). In other words, DDR2 memory each clock can read/write data at 4 times times the speed of the external bus, and can run at 4 times times the speed of the internal control bus.

Working principle:

DDR memory technology, so that memory can be in the clock's rise and fall phase of each transmission of data, that is, a clock cycle of two data transmission, DDR2 memory technology is delayed more than 1 time times, in two clock cycle of four times, and each data transmission in 4bit, That is, one more clock cycle than the DDR memory is sacrificed to run at 4 times times the speed.

DDR2 has also introduced three new technologies:

OCD (off-chip Driver): The so-called off-line drive adjustment, DDR II through the OCD can improve signal integrity. DDR II makes both voltages equal by adjusting the resistance values of the pull/pull. Use OCD to improve signal integrity by reducing the tilt of the Dq-dqs, and to improve signal quality by controlling voltage.

Odt:odt is a built-in core of the end resistor. DDR2 can be built according to the characteristics of the appropriate termination resistance, so as to ensure the best signal waveform. Using DDR2 can not only reduce the cost of the motherboard, but also get the best signal quality.

Post CAS: It is set up to increase the utilization efficiency of DDR II memory. So that the act and CAS signals never have collision conflicts.