52 www.xilinx.comSpartan-3A/3AN FPGA Starter Kit Board User GuideUG334 (v1.1) June 19, 2008Chapter 5: Character LCD Screen RAfter the write operation, the address is automatically incremented or decremented by 1according to the Entry Mode Set command. The entry mode also determines display shift.Execution Time: 40 μsRead Data from CG RAM or DD RAMReads data from DD RAM if the command follows a previous Set DD RAM Addresscommand, or reads data from CG RAM if the command follows a previous Set CG RAMAddress command.After the read operation, the address is automatically incremented or decremented by 1according to the Entry Mode Set command. However, a display shift is not executedduring read operations.Execution Time: 40 μsOperationThe board has an eight-bit data interface to the character LCD. Other Xilinx boards use afour-bit interface. As shown in Figure 5-1, the Spartan-3A/3AN Starter Kit board supportsboth an eight-bit and a four-bit interface for compatibility reasons. Many existing referencedesigns are already built around a four-bit interface.Four-Bit Data InterfaceFigure 5-6 illustrates a write operation to the LCD, showing the minimum times allowedfor setup, hold, and enable pulse length relative to the 50 MHz clock (20 ns period)provided on the board.
