📄 lcd.fmt
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RETURN
;
;Delay of 20ms.
;
;Delay of 20ms used during initialisation.
;
;Registers used s0, s1, s2, s3
;
delay_20ms: LOAD s3, 14 ;20 x 1ms = 20ms
wait_20ms: CALL delay_1ms
SUB s3, 01
JUMP NZ, wait_20ms
RETURN
;
;Delay of approximately 1 second.
;
;Registers used s0, s1, s2, s3, s4
;
delay_1s: LOAD s4, 32 ;50 x 20ms = 1000ms
wait_1s: CALL delay_20ms
SUB s4, 01
JUMP NZ, wait_1s
RETURN
;
;
;
;**************************************************************************************
;LCD Character Module Routines
;**************************************************************************************
;
;LCD module is a 16 character by 2 line display but all displays are very similar
;The 4-wire data interface will be used (DB4 to DB7).
;
;The LCD modules are relatively slow and software delay loops are used to slow down
;KCPSM3 adequately for the LCD to communicate. The delay routines are provided in
;a different section (see above in this case).
;
;
;Pulse LCD enable signal 'E' high for greater than 230ns (1us is used).
;
;Register s4 should define the current state of the LCD output port.
;
;Registers used s0, s4
;
LCD_pulse_E: XOR s4, LCD_E ;E=1
OUTPUT s4, LCD_output_port
CALL delay_1us
XOR s4, LCD_E ;E=0
OUTPUT s4, LCD_output_port
RETURN
;
;Write 4-bit instruction to LCD display.
;
;The 4-bit instruction should be provided in the upper 4-bits of register s4.
;Note that this routine does not release the master enable but as it is only
;used during initialisation and as part of the 8-bit instruction write it
;should be acceptable.
;
;Registers used s4
;
LCD_write_inst4: AND s4, F8 ;Enable=1 RS=0 Instruction, RW=0 Write, E=0
OUTPUT s4, LCD_output_port ;set up RS and RW >40ns before enable pulse
CALL LCD_pulse_E
RETURN
;
;
;Write 8-bit instruction to LCD display.
;
;The 8-bit instruction should be provided in register s5.
;Instructions are written using the following sequence
; Upper nibble
; wait >1us
; Lower nibble
; wait >40us
;
;Registers used s0, s1, s4, s5
;
LCD_write_inst8: LOAD s4, s5
AND s4, F0 ;Enable=0 RS=0 Instruction, RW=0 Write, E=0
;OR s4, LCD_drive ;Enable=1
CALL LCD_write_inst4 ;write upper nibble
CALL delay_1us ;wait >1us
LOAD s4, s5 ;select lower nibble with
SL1 s4 ;Enable=1
SL0 s4 ;RS=0 Instruction
SL0 s4 ;RW=0 Write
SL0 s4 ;E=0
CALL LCD_write_inst4 ;write lower nibble
CALL delay_40us ;wait >40us
LOAD s4, F0 ;Enable=0 RS=0 Instruction, RW=0 Write, E=0
OUTPUT s4, LCD_output_port ;Release master enable
RETURN
;
;
;
;Write 8-bit data to LCD display.
;
;The 8-bit data should be provided in register s5.
;Data bytes are written using the following sequence
; Upper nibble
; wait >1us
; Lower nibble
; wait >40us
;
;Registers used s0, s1, s4, s5
;
LCD_write_data: LOAD s4, s5
AND s4, F0 ;Enable=0 RS=0 Instruction, RW=0 Write, E=0
OR s4, 0C ;Enable=1 RS=1 Data, RW=0 Write, E=0
OUTPUT s4, LCD_output_port ;set up RS and RW >40ns before enable pulse
CALL LCD_pulse_E ;write upper nibble
CALL delay_1us ;wait >1us
LOAD s4, s5 ;select lower nibble with
SL1 s4 ;Enable=1
SL1 s4 ;RS=1 Data
SL0 s4 ;RW=0 Write
SL0 s4 ;E=0
OUTPUT s4, LCD_output_port ;set up RS and RW >40ns before enable pulse
CALL LCD_pulse_E ;write lower nibble
CALL delay_40us ;wait >40us
LOAD s4, F0 ;Enable=0 RS=0 Instruction, RW=0 Write, E=0
OUTPUT s4, LCD_output_port ;Release master enable
RETURN
;
;
;
;Reset and initialise display to communicate using 4-bit data mode
;Includes routine to clear the display.
;
;Requires the 4-bit instructions 3,3,3,2 to be sent with suitable delays
;following by the 8-bit instructions to set up the display.
;
; 28 = '001' Function set, '0' 4-bit mode, '1' 2-line, '0' 5x7 dot matrix, 'xx'
; 06 = '000001' Entry mode, '1' increment, '0' no display shift
; 0E = '00001' Display control, '1' display on, '1' cursor off, '0' cursor blink off
; 01 = '00000001' Display clear
;
;Registers used s0, s1, s2, s3, s4
;
LCD_reset: CALL delay_20ms ;wait more that 15ms for display to be ready
LOAD s4, 30
CALL LCD_write_inst4 ;send '3'
CALL delay_20ms ;wait >4.1ms
CALL LCD_write_inst4 ;send '3'
CALL delay_1ms ;wait >100us
CALL LCD_write_inst4 ;send '3'
CALL delay_40us ;wait >40us
LOAD s4, 20
CALL LCD_write_inst4 ;send '2'
CALL delay_40us ;wait >40us
LOAD s5, 28 ;Function set
CALL LCD_write_inst8
LOAD s5, 06 ;Entry mode
CALL LCD_write_inst8
LOAD s5, 0E ;Display control
CALL LCD_write_inst8
LCD_clear: LOAD s5, 01 ;Display clear
CALL LCD_write_inst8
CALL delay_1ms ;wait >1.64ms for display to clear
CALL delay_1ms
RETURN
;
;Position the cursor ready for characters to be written.
;The display is formed of 2 lines of 16 characters and each
;position has a corresponding address as indicated below.
;
; Character position
; 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
;
; Line 1 - 80 81 82 83 84 85 86 87 88 89 8A 8B 8C 8D 8E 8F
; Line 2 - C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 CA CB CC CD CE CF
;
;This routine will set the cursor position using the value provided
;in register s5. The upper nibble will define the line and the lower
;nibble the character position on the line.
; Example s5 = 2B will position the cursor on line 2 position 11
;
;Registers used s0, s1, s2, s3, s4
;
LCD_cursor: TEST s5, 10 ;test for line 1
JUMP Z, set_line2
AND s5, 0F ;make address in range 80 to 8F for line 1
OR s5, 80
CALL LCD_write_inst8 ;instruction write to set cursor
RETURN
set_line2: AND s5, 0F ;make address in range C0 to CF for line 2
OR s5, C0
CALL LCD_write_inst8 ;instruction write to set cursor
RETURN
;
;This routine will shift the complete display one position to the left.
;The cursor position and LCD memory contents will not change.
;
;
;Registers used s0, s1, s2, s3, s4, s5
;
LCD_shift_left: LOAD s5, 18 ;shift display left
CALL LCD_write_inst8
RETURN
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