Due to its small size, light weight, and low power consumption, LCD liquid crystal displays are used in a wide range of applications. For example, as display panels for aircrafts, tanks, and ships, the space occupied by original CRT displays can be reduced, equipment weight can be reduced, and maneuverability can be enhanced.
This design uses a character LCD with an embedded Si.tronix ST7066U graphic controller on the Spartan-3E development board, which implements: (1) Single character display at any position and full-screen and full-screen display of characters; (2) The display of custom characters (characters) and the full screen movement display of individual characters. Among them, the graphic controller [1] is responsible for receiving control commands and data and sending it to the LCD display.
1 Sitronix ST7066U Graphics Controller
The controller has three internal storage spaces, DD RAM, CGROM, and CG RAM, which should be initialized before sending data.
(1) DD RAM (display data RAM)
The character code is stored. Physically, the DD RAM has a total of 80 character positions, each line has 40 characters, but only 16 can be displayed and the remaining 24 are not displayed. Before reading or writing, the address counter needs to be initialized. The address counter can be kept constant or automatically incremented or decremented by 1 after reading or writing.
(2) CG ROM (Character Generator ROM)
A font bitmap containing each pre-determined character.
(3) CG RAM (character generator RAM)
Contains 8-bit custom character bitmaps. Each custom character bit consists of 5 points in 8-bit bitmaps. The specific usage is the same as DD RAM.
1.1 Interface Signals with FPGA
LCD and FPGA interface signals [2] are: (1) enable signal LCD_E; (2) register select signal LCD_RS; (3) read/write control signal LCD_RW; (4) four LCD data lines and StrataFlash data line SF_D <11:8> Multiplexing.
1.2 Timing Analysis
The data value of SF_D<11:8>, LCD_RS, LCD_RW must be established and stable for at least 40 ns before LCD_E goes high, and LCD_E remains high for at least 230 ns. In many applications, LCD_RW is always low because data is not normally read from the display.
