What is zq calibration in ddr3

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Welcome to EDAboard. To participate you need to register. Registration is free. There are two parameters exisited in the ZQ calibration commands. ZQCL is used to perform the initial calibration during power-up initialization sequences. ZQCL can be issued at anytime, it's up to the controller and the system enviroment. ZQCS, It accurately correct the a minimum of 0.

So the interval between ZQCS command is calcuated as : 0. But spec told us that the total capacitive loading on the ZQ pin must be limited. The following sections go into more detail about what the controller does when you enable each of these algorithms.

If tDQSS is violated and falls outside the range, wrong data may be written to the memory. When you enable write-leveling in the controller, it does the following steps: Does an Mode Register write to MR1 to set bit 7 to 1. This puts the DRAM into write-leveling mode.

The controller then sends a series of DQS pulses. It is typically a step that is performed before Read Centering and Write Centering. The purpose of read centering is to train the internal read capture circuitry in the controller or PHY to capture the data in the center of the data eye. Then initiates a continuous stream of READs.

Let's assume this pattern is an alternating While the READs are going on, the internal read capture circuitry either increases of decreases an internal read delay register to find the left and right edge of the data eye. When the edges of the eye are detected, the read delay registers are set appropriately to ensure the data is captured at the eye center. The above steps are repeated for each of the DQ data bits.

Similar to the read centering step, the purpose of write centering is to set the write delay for each data bit so that write data is centered on the corresponding write strobe edge at the DRAM device.

From the above loop the PHY can determine for what write-delay range it reads back good data, and hence it can figure out the left and write edges of the write-data eye. In a device such as a network switch or router, there could be changes in Voltage and Temperature during its course of operation.

Periodic Read Centering - To re-calculate read delays and other read related parameters. Typically, the memory controller or PHY allow you to set a timer and enable periodic calibration through their registers. Once the timer is set, periodic calibration is run every time the timer expires. Once this is done system is officially in IDLE and operational. You may need to enable periodic calibration depending upon the conditions in which your device is deployed.