LCD_Notes_4-bit - University of Florida Dept. of Electrical...

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University of Florida EEL4744 Dr. Eric M. Schwartz Dept. of Electrical and Computer Engineering John A. Martiney, TA Page 1/7 Revision 2 17-Mar-11 4-bit LCD Interface Notes 10 LCD LCD Board Pinout 1 D3-0 A0 R/W P V DD V O V SS DB7-4 RS R/W LCD E CPU Decode Circuitry P / LCD Wiring diagram Potentiometer LCD Panel Pinouts and Connections to CPU (for data bus connectivity) Verify that the position of pin 1 on your LCD board. There should be a 1 next to pin 1 and a 10 next to pin 10. My LCD board is arranged as shown to the right. The register select signal (RS) can be viewed as an address input and can be connected directly to the CPU’s address pin A 0 . This bit selects between the two addressable registers called Command (with A 0 =0) and Data (with A 0 =1). The enable pin (E) is the chip select/enable for the LCD. A memory mapped decoded E signal must be created for enabling/disabling this device. The LCD can be considered a write-only device. [If you want to read from the device, DB7 is the busy flag (BF) that when clear means the LCD is ready for the next command. If this is done the delays in the below flow chart are unnecessary.] You can verify that your LCD works properly before connecting your LCD data pins. Give power to the device and twist the potentiometer one way or the other until you see black lines appear. Data or commands are read at the falling edge of E . From the Densitron LM2022 LCD specifications posted on our website. Parameter (in ns) Symbol Min Max Enable Cycle Time T CYC 500 Enable Pulse Width PW EH 230 Enable Rise/Fall Time t Er / t Ef 20 Address Setup Time t AS 40 Address Hold Time t AH 10 Write Data Setup Time t DSW 80 Write Data Hold Time t DHW 10
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University of Florida EEL4744 Dr. Eric M. Schwartz Dept. of Electrical and Computer Engineering John A. Martiney, TA Page 2/7 Revision 2 17-Mar-11 4-bit LCD Interface Notes Important Notes regarding 4-bit mode: The difference between 4-bit and 8-bit LCD operation is that data is sent out as nibbles instead of a single byte . DB7:DB4 are used to transfer nibbles to/from the LCD module (DB7 is the MSB). Commands and data are still 8 bits long, but are transferred as two 4-bit nibbles on the LCD data bus lines DB7:DB4. The most significant nibble
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LCD_Notes_4-bit - University of Florida Dept. of Electrical...

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