pato-z80-home-computer/assembly/pat80_bios_0.1.asm

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; Pat80 BIOS v0.01
; @author: Daniele Verducci
;
; ROM is at 0x00
; RAM is at 0x80
; LCD is at I/O 0x00 and 0x01
jp sysinit ; Startup vector: DO NOT MOVE! Must be the first instruction
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; SYSTEM CONFIGURATION
LCD_INSTR_REG: EQU %00000000
LCD_DATA_REG: EQU %00000001
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; CONSTANTS
SYSINIT_GREETING:
DB "Pat80 BIOS v0.1 ",0 ; null terminated string
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; System initialization
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sysinit:
call lcd_init
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; write characters to display
ld bc, SYSINIT_GREETING
call lcd_write ; write string to screen
call lcd_cls ; clear screen
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halt
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lcd_init:
;reset procedure
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ld a,0x38
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out (LCD_INSTR_REG),a
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ld a,0x08
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out (LCD_INSTR_REG),a
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ld a,0x01
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out (LCD_INSTR_REG),a
;init procedure
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ld a,0x38
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out (LCD_INSTR_REG),a
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ld a,0x0F
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out (LCD_INSTR_REG),a
ret
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; Writes text starting from current cursor position
; @param BC Pointer to a null-terminated string first character
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lcd_write:
ld a, (bc) ; bc is the pointer to passed string's first char
cp 0 ; compare A content with 0 (subtract 0 from value and set zero flag Z if result is 0)
ret z ; if prev compare is true (Z flag set), string is finished, return
out (LCD_DATA_REG),a ; output char
inc bc ; increment bc to move to next char
jp lcd_write
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; Set cursor position
; @param B X-axis position (0 to 19)
; @param C Y-axis position (0 to 3)
lcd_locate:
; TODO
ret
; Clears the screen
lcd_cls:
ld a,0x01
out (LCD_INSTR_REG),a ; clear display
ld a,0x02
out (LCD_INSTR_REG),a ; cursor to home (top left)
ret