The DDR (Double Data Rate) interface is commonly used in computer memory systems to facilitate high-speed data transfer between the processor and memory modules. It employs a technique called "double pumping" to transfer data on both the rising and falling edges of the clock signal, effectively doubling the data transfer rate compared to a single data rate interface.
In both read and write operations, the DDR interface follows a similar process, involving specific commands and signaling mechanisms.
Let's break down the steps for both read and write operations in following Slides
Read Operation:
Command and Address Setup:
The processor sends a read command along with the memory address of the desired data to the DDR interface.
Row Activation:
The DDR interface activates the memory row corresponding to the provided address, allowing access to the stored data.
Column Address Strobe (CAS):
The DDR interface sends the column address, specifying the exact location of the data within the activated row.
Data Transfer:
The DDR interface transfers the requested data from the memory module to the processor. The data is typically sent in bursts, with multiple data words being transferred in sequence.
Read Latency:
There may be a latency period between the CAS command and the actual data transfer due to internal operations within the memory module. This latency allows the memory to perform necessary tasks before sending the data.
Data Reception:
The processor receives the transferred data and processes it accordingly.
Write Operation:
Command and Address Setup:
The processor sends a write command along with the memory address where the data should be written.
Row Activation:
The DDR interface activates the memory row corresponding to the provided address, preparing it for data storage.
Column Address Strobe (CAS):
The DDR interface sends the column address, specifying the exact location within the activated row where the data should be written.
Data Transfer:
The processor sends the data to be written to the DDR interface, which stores it in the specified memory location. As with read operations, the data is typically transferred in bursts.
Write Latency:
Similar to read operations, there may be a latency period between the CAS command and the actual data transfer for internal memory operations.
Data Confirmation:
After the data has been written, the DDR interface may send a confirmation signal back to the processor to indicate the completion of the write operation.
In both read and write operations, the DDR interface leverages the double data rate technique, allowing data to be transferred on both the rising and falling edges of the clock signal. This doubling of the data transfer rate significantly enhances the overall memory bandwidth and system performance.