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351 lines
7.2 KiB
NASM
351 lines
7.2 KiB
NASM
; lcd
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;
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; Implement PutC on TI-84+ (for now)'s LCD screen.
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;
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; The screen is 96x64 pixels. The 64 rows are addressed directly with CMD_ROW
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; but columns are addressed in chunks of 6 or 8 bits (there are two modes).
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;
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; In 6-bit mode, there are 16 visible columns. In 8-bit mode, there are 12.
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;
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; Note that "X-increment" and "Y-increment" work in the opposite way than what
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; most people expect. Y moves left and right, X moves up and down.
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;
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; *** Z-Offset ***
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;
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; This LCD has a "Z-Offset" parameter, allowing to offset rows on the
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; screen however we wish. This is handy because it allows us to scroll more
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; efficiently. Instead of having to copy the LCD ram around at each linefeed
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; (or instead of having to maintain an in-memory buffer), we can use this
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; feature.
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;
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; The Z-Offet goes upwards, with wrapping. For example, if we have an 8 pixels
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; high line at row 0 and if our offset is 8, that line will go up 8 pixels,
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; wrapping itself to the bottom of the screen.
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;
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; The principle is this: The active line is always the bottom one. Therefore,
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; when active row is 0, Z is FNT_HEIGHT+1, when row is 1, Z is (FNT_HEIGHT+1)*2,
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; When row is 8, Z is 0.
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;
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; *** 6/8 bit columns and smaller fonts ***
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;
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; If your glyphs, including padding, are 6 or 8 pixels wide, you're in luck
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; because pushing them to the LCD can be done in a very efficient manner.
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; Unfortunately, this makes the LCD unsuitable for a Collapse OS shell: 6
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; pixels per glyph gives us only 16 characters per line, which is hardly
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; usable.
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;
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; This is why we have this buffering system. How it works is that we're always
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; in 8-bit mode and we hold the whole area (8 pixels wide by FNT_HEIGHT high)
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; in memory. When we want to put a glyph to screen, we first read the contents
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; of that area, then add our new glyph, offsetted and masked, to that buffer,
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; then push the buffer back to the LCD. If the glyph is split, move to the next
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; area and finish the job.
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;
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; That being said, it's important to define clearly what CURX and CURY variable
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; mean. Those variable keep track of the current position *in pixels*, in both
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; axes.
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;
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; *** Requirements ***
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; fnt/mgm
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;
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; *** Constants ***
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.equ LCD_PORT_CMD 0x10
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.equ LCD_PORT_DATA 0x11
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.equ LCD_CMD_6BIT 0x00
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.equ LCD_CMD_8BIT 0x01
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.equ LCD_CMD_DISABLE 0x02
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.equ LCD_CMD_ENABLE 0x03
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.equ LCD_CMD_XDEC 0x04
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.equ LCD_CMD_XINC 0x05
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.equ LCD_CMD_YDEC 0x06
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.equ LCD_CMD_YINC 0x07
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.equ LCD_CMD_COL 0x20
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.equ LCD_CMD_ZOFFSET 0x40
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.equ LCD_CMD_ROW 0x80
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.equ LCD_CMD_CONTRAST 0xc0
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; *** Variables ***
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; Current Y position on the LCD, that is, where re're going to spit our next
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; glyph.
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.equ LCD_CURY LCD_RAMSTART
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; Current X position
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.equ LCD_CURX @+1
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; two pixel buffers that are 8 pixels wide (1b) by FNT_HEIGHT pixels high.
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; This is where we compose our resulting pixels blocks when spitting a glyph.
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.equ LCD_BUF @+1
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.equ LCD_RAMEND @+FNT_HEIGHT*2
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; *** Code ***
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lcdInit:
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; Initialize variables
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xor a
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ld (LCD_CURY), a
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ld (LCD_CURX), a
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; Clear screen
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call lcdClrScr
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; We begin with a Z offset of FNT_HEIGHT+1
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ld a, LCD_CMD_ZOFFSET+FNT_HEIGHT+1
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call lcdCmd
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; Enable the LCD
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ld a, LCD_CMD_ENABLE
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call lcdCmd
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; Hack to get LCD to work. According to WikiTI, we're not sure why TIOS
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; sends these, but it sends it, and it is required to make the LCD
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; work. So...
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ld a, 0x17
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call lcdCmd
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ld a, 0x0b
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call lcdCmd
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; Set some usable contrast
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ld a, LCD_CMD_CONTRAST+0x34
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call lcdCmd
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; Enable 8-bit mode.
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ld a, LCD_CMD_8BIT
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call lcdCmd
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ret
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; Wait until the lcd is ready to receive a command
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lcdWait:
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push af
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.loop:
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in a, (LCD_PORT_CMD)
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; When 7th bit is cleared, we can send a new command
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rla
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jr c, .loop
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pop af
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ret
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; Send cmd A to LCD
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lcdCmd:
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out (LCD_PORT_CMD), a
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jr lcdWait
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; Send data A to LCD
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lcdDataSet:
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out (LCD_PORT_DATA), a
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jr lcdWait
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; Get data from LCD into A
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lcdDataGet:
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in a, (LCD_PORT_DATA)
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jr lcdWait
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; Turn LCD off
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lcdOff:
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push af
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ld a, LCD_CMD_DISABLE
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call lcdCmd
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out (LCD_PORT_CMD), a
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pop af
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ret
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; Set LCD's current column to A
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lcdSetCol:
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push af
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; The col index specified in A is compounded with LCD_CMD_COL
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add a, LCD_CMD_COL
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call lcdCmd
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pop af
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ret
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; Set LCD's current row to A
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lcdSetRow:
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push af
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; The col index specified in A is compounded with LCD_CMD_COL
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add a, LCD_CMD_ROW
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call lcdCmd
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pop af
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ret
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; Send the glyph that HL points to to the LCD, at its current position.
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; After having called this, the LCD's position will have advanced by one
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; position
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lcdSendGlyph:
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push af
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push bc
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push hl
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push ix
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ld a, (LCD_CURY)
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call lcdSetRow
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ld a, (LCD_CURX)
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srl a \ srl a \ srl a ; div by 8
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call lcdSetCol
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; First operation: read the LCD memory for the "left" side of the
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; buffer. We assume the right side to always be empty, so we don't
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; read it. After having read each line, compose it with glyph line at
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; HL
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; Before we start, what is our bit offset?
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ld a, (LCD_CURX)
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and 0b111
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; that's our offset, store it in C
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ld c, a
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ld a, LCD_CMD_XINC
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call lcdCmd
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ld ix, LCD_BUF
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ld b, FNT_HEIGHT
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; A dummy read is needed after a movement.
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call lcdDataGet
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.loop1:
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; let's go get that glyph data
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ld a, (hl)
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ld (ix), a
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call .shiftIX
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; now let's go get existing pixel on LCD
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call lcdDataGet
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; and now let's do some compositing!
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or (ix)
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ld (ix), a
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inc hl
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inc ix
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djnz .loop1
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; Buffer set! now let's send it.
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ld a, (LCD_CURY)
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call lcdSetRow
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ld hl, LCD_BUF
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ld b, FNT_HEIGHT
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.loop2:
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ld a, (hl)
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call lcdDataSet
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inc hl
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djnz .loop2
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; And finally, let's send the "right side" of the buffer
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ld a, (LCD_CURY)
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call lcdSetRow
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ld a, (LCD_CURX)
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srl a \ srl a \ srl a ; div by 8
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inc a
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call lcdSetCol
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ld hl, LCD_BUF+FNT_HEIGHT
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ld b, FNT_HEIGHT
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.loop3:
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ld a, (hl)
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call lcdDataSet
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inc hl
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djnz .loop3
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; Increase column and wrap if necessary
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ld a, (LCD_CURX)
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add a, FNT_WIDTH+1
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ld (LCD_CURX), a
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cp 96-FNT_WIDTH
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jr c, .skip ; A < 96-FNT_WIDTH
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call lcdLinefeed
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.skip:
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pop ix
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pop hl
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pop bc
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pop af
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ret
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; Shift glyph in (IX) to the right C times, sending carry into (IX+FNT_HEIGHT)
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.shiftIX:
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dec c \ inc c
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ret z ; zero? nothing to do
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push bc ; --> lvl 1
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xor a
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ld (ix+FNT_HEIGHT), a
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.shiftLoop:
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srl (ix)
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rr (ix+FNT_HEIGHT)
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dec c
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jr nz, .shiftLoop
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pop bc ; <-- lvl 1
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ret
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; Changes the current line and go back to leftmost column
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lcdLinefeed:
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push af
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ld a, (LCD_CURY)
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call .addFntH
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ld (LCD_CURY), a
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call lcdClrLn
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; Now, lets set Z offset which is CURROW+FNT_HEIGHT+1
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call .addFntH
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add a, LCD_CMD_ZOFFSET
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call lcdCmd
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xor a
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ld (LCD_CURX), a
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pop af
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ret
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.addFntH:
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add a, FNT_HEIGHT+1
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cp 64
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ret c ; A < 64? no wrap
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; we have to wrap around
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xor a
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ret
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; Clears B rows starting at row A
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; B is not preserved by this routine
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lcdClrX:
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push af
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call lcdSetRow
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.outer:
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push bc ; --> lvl 1
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ld b, 11
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ld a, LCD_CMD_YINC
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call lcdCmd
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xor a
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call lcdSetCol
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.inner:
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call lcdDataSet
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djnz .inner
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ld a, LCD_CMD_XINC
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call lcdCmd
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xor a
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call lcdDataSet
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pop bc ; <-- lvl 1
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djnz .outer
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pop af
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ret
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lcdClrLn:
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push bc
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ld b, FNT_HEIGHT+1
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call lcdClrX
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pop bc
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ret
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lcdClrScr:
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push bc
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ld b, 64
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call lcdClrX
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pop bc
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ret
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lcdPutC:
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cp LF
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jp z, lcdLinefeed
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cp BS
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jr z, .bs
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push hl
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call fntGet
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jr nz, .end
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call lcdSendGlyph
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.end:
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pop hl
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ret
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.bs:
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ld a, (LCD_CURX)
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or a
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ret z ; going back one line is too complicated.
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; not implemented yet
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sub FNT_WIDTH+1
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ld (LCD_CURX), a
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ret
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