Thursday, November 8, 2012

LCD 16x2 PIC16F690

HD44780 - LCD

On today's article we are going to use an lcd 16x2 with Hitachi HD44780 LCD controller.
wikipedia image

It is necessary before we proceed with schematics and code to explain the basics of these lcds.

Pins

lcd display 16x2

  1. Vss - Ground
  2. Vdd - 5 volts
  3. Vee - contrast adjustment
  4. RS - register select
  5. RW - read or write
  6. E - enable
  7. D0-D7: is the data/command pins
  8. Vdd - backlight anode (optional)
  9. Vss - backlight cathode (optional)
The first 3 pins is just for power. 

The fourth pin RS, is the register select pin. If this is set (RS=1) it means that the data register is selected and the display is now waiting for data. But if RS is unset (RS=0) the command register is selected and the Lcd is waiting for commands to be appeared between D0-D7 pins. That pin it is very important because throughout our projects is very common to send both data and commands.

The fifth pin RW,is the read/write register. When is set (RW=1) we can read from the lcd (rare but is it possible), and when is unset (RW=0) we can write to lcd.

The sixth pin E, enable, it is used as a flag for the lcd to show that the data/command on the D0-D7 pins is valid, and the data/command will be latched into lcd controller as soon as this pin change from high to low. For example if i want to write 10001001, i should move to PORTC the value 10001001, and the data will be valid only when a high to low pulse appears to Enable pin.

The seventh is the data/command pins D0-D7. The valid commands is available in the datasheet of the display, and the data it will be ascii code of the character. For example if i want to write the letter "A" on the display i should apply to the D0-D7 pins the code 0x41 which the ascii equivalent code of "A".

Initialization

The initialization it can be happen by following the flow chart below:


Every part of the flow chart is a command we can send to the display based on the table below:


Keep in mind that in order to send a command (or data) we have to follow the flowchart below:
Here is the initialization code:


  1. Lcd_Init
  2. ;RB4 -->  RS
  3. ;RB5 -->  RW
  4. ;RB6 -->  E
  5. ;RC0-RC7  --> D0-D7

  7. ;wait for the LCD display to boot up
  8. call Delay100ms
  9. ;ready for command
  10. bcf PORTB, 4

  12. ;1. Clear Display and Home the Cursor
  13. ;movlw b'00000001'
  14. movwf PORTC
  15. bsf PORTB, 6
  16. call Delay1ms
  17. bcf PORTB, 6
  18. call Delay1ms

  20. ;2. Return Cursor and LCD to Home Position
  21. movlw b'00000010'
  22. movwf PORTC
  23. bsf PORTB, 6
  24. call Delay1ms
  25. bcf PORTB, 6
  26. call Delay1ms

  28. ;3. Set Cursor Move Direction
  29. ;0-0-0-0-0-1-ID-S
  30. ;ID - Increment the Cursor After Each Byte Written to Display if Set
  31. ;S - Shift Display when Byte Written to Display
  32. movlw b'00000110'
  33. movwf PORTC
  34. bsf PORTB, 6
  35. call Delay1ms
  36. bcf PORTB, 6
  37. call Delay1ms

  39. ;4. Enable Display/Cursor
  40. ;0-0-0-0-1-D-C-B
  41. ;D - Turn Display On(1)/Off(0)
  42. ;C - Turn Cursor On(1)/Off(0)
  43.   ;B - Cursor Blink On(1)/Off(0)
  44. movlw b'00001111'
  45. movwf PORTC
  46. bsf PORTB, 6
  47. call Delay1ms
  48. bcf PORTB, 6
  49. call Delay1ms

  51. ;5. Move Cursor/Shift Display
  52. ;0-0-0-1-SC-RL-x-x
  53. ;SC - Display Shift On(1)/Off(0)
  54.   ;RL - Direction of Shift Right(1)/Left(0)
  55. movlw b'00010100'
  56. movwf PORTC
  57. bsf PORTB, 6
  58. call Delay1ms
  59. bcf PORTB, 6
  60. call Delay1ms
  62. ;6. Set Interface Length
  63. ;0-0-1-DL-N-F-*-*
  64. ;DL - Set Data Interface Length 8(1)/4(0)
  65. ;N - Number of Display Lines 1(0)/2(1)
  66. ;F - Character Font 5x10(1)/5x7(0)
  67. movlw b'00111100'
  68. movwf PORTC
  69. bsf PORTB, 6
  70. call Delay1ms
  71. bcf PORTB, 6
  72. call Delay1ms

  74. ;7.
  75. bcf PORTB, 5
  76. movlw 0x80
  77. movwf PORTC
  78. bsf PORTB, 6
  79. call Delay1ms
  80. bcf PORTB, 6
  81. call Delay1ms

  83. return

Schematic

So based on the explanation above, we created the following schematic:


Message

And after the initialization ends, we are now ready to write the message we want on the screen:


  1. ...
  2. SPACE_l EQU 0x20
  3. A_l EQU 0x41
  4. B_l EQU 0x42
  5. C_l EQU 0x43
  6. D_l EQU 0x44
  7. E_l EQU 0x45
  8. F_l EQU 0x46
  9. G_l EQU 0x47
  10. H_l EQU 0x48
  11. I_l EQU 0x49
  12. J_l EQU 0x4A
  13. K_l EQU 0x4B
  14. L_l EQU 0x4C
  15. M_l EQU 0x4D
  16. N_l EQU 0x4E
  17. O_l EQU 0x4F
  18. P_l EQU 0x50
  19. Q_l EQU 0x51
  20. R_l EQU 0x52
  21. S_l EQU 0x53
  22. T_l EQU 0x54
  23. U_l EQU 0x55
  24. V_l EQU 0x56
  25. W_l EQU 0x57
  26. X_l EQU 0x58
  27. Y_l EQU 0x59
  28. Z_l EQU 0x5A
  29. ...

  31. ;write data
  32. bsf PORTB, 4

  34. movlw H_l
  35. movwf PORTC
  36. bsf PORTB, 6
  37. call Delay100us
  38. bcf PORTB, 6

  40. movlw E_l
  41. movwf PORTC
  42. bsf PORTB, 6
  43. call Delay100us
  44. bcf PORTB, 6

  46. movlw L_l
  47. movwf PORTC
  48. bsf PORTB, 6
  49. call Delay100us
  50. bcf PORTB, 6

  52. movlw L_l
  53. movwf PORTC
  54. bsf PORTB, 6
  55. call Delay100us
  56. bcf PORTB, 6

  58. movlw O_l
  59. movwf PORTC
  60. bsf PORTB, 6
  61. call Delay100us
  62. bcf PORTB, 6

  64. ;move cursor to line 2
  65. bcf PORTB, 4 ;write command
  66. bcf PORTB, 5
  67. movlw 0xC0
  68. movwf PORTC
  69. bsf PORTB, 6
  70. call Delay1ms
  71. bcf PORTB, 6
  72. call Delay1ms

  75. ;write data
  76. bsf PORTB, 4

  78. movlw J_l
  79. movwf PORTC
  80. bsf PORTB, 6
  81. call Delay100us
  82. bcf PORTB, 6

  84. movlw A_l
  85. movwf PORTC
  86. bsf PORTB, 6
  87. call Delay100us
  88. bcf PORTB, 6

  90. movlw C_l
  91. movwf PORTC
  92. bsf PORTB, 6
  93. call Delay100us
  94. bcf PORTB, 6

  96. movlw K_l
  97. movwf PORTC
  98. bsf PORTB, 6
  99. call Delay100us
  100. bcf PORTB, 6

  102. movlw SPACE_l
  103. movwf PORTC
  104. bsf PORTB, 6
  105. call Delay100us
  106. bcf PORTB, 6

  108. movlw S_l
  109. movwf PORTC
  110. bsf PORTB, 6
  111. call Delay100us
  112. bcf PORTB, 6

  114. movlw P_l
  115. movwf PORTC
  116. bsf PORTB, 6
  117. call Delay100us
  118. bcf PORTB, 6

  120. movlw A_l
  121. movwf PORTC
  122. bsf PORTB, 6
  123. call Delay100us
  124. bcf PORTB, 6

  126. movlw R_l
  127. movwf PORTC
  128. bsf PORTB, 6
  129. call Delay100us
  130. bcf PORTB, 6

  132. movlw R_l
  133. movwf PORTC
  134. bsf PORTB, 6
  135. call Delay100us
  136. bcf PORTB, 6
  138. movlw O_l
  139. movwf PORTC
  140. bsf PORTB, 6
  141. call Delay100us
  142. bcf PORTB, 6

  144. movlw W_l
  145. movwf PORTC
  146. bsf PORTB, 6
  147. call Delay100us
  148. bcf PORTB, 6

  150. loop
  151. goto loop

All the files can be found here...

Thank you...
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