Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

3.5.5.7.1. Half-Rate Mode

Half-rate mode is optimal in cases where you require the highest possible SDRAM clock frequency, or when the complexity of your system logic means that you are not able to achieve the clock frequency you need for the DDR SDRAM. In half-rate mode, the internal Avalon® interface to the SDRAM controller runs at half the external SDRAM frequency.

In half-rate mode, the local data width (the data width inside the Platform Designer system) of the SDRAM controller is four times the data width of the physical DDR SDRAM device. For example, if your SDRAM device is 8 bits wide, the internal Avalon® data port of the SDRAM controller is 32 bits. This design choice facilitates bursts of four accesses to the SDRAM device.