Tutorial 7
Displaying Text

Overview

This tutorial will show you how to make a program that will display normal and inverse (white on black) text.

Programming

The program below will display normal text on the home screen. The program uses the calls we have already learned, and adds some new ones. In a future tutorial, we will make a program that displays small text.

#define B_CALL(xxxx)	rst 28h \ .dw xxxx		
#define B_JUMP(xxxx)	call 50h \ .dw xxxx	

_clrlcdfull		=4540h			;The calls we will be using are defined here or use an include file
_homeup		=4558h
_puts		=450Ah
CURCOL		=800Dh
CURROW	=800Ch
	
	.org 9D95h	
	
	B_CALL(_clrlcdfull)				;Clear the screen
	B_CALL(_homeup) 			;Bring on the home screen
	ld	a,0				;Load "a" register as zero 
	ld	(CURCOL),a			;Load zero into the y coordinate
	ld	(CURROW),a			;Load zero into the x coordinate
	ld	hl,txtLabel			;Load text from label below
	B_CALL(_puts)				;Put text on screen
	B_CALL(_clrlcdfull)				;Clear screen
	ret					;Return to OS
txtLabel:					;the "Label" can be replaced with any name you want as long as you change the one on the top
	.db	"This Program    " 			
	.db	"displays text      " 			
	.db	"on the home     "
	.db	"screen. It can   "
	.db	"be up to 16 char"
	.db	"long, it     can  "
	.db	"only be 8 lines  "
	.db	"long.	          ",0	
.end						
END

New Commands Used

(CURCOL) - the y coordinate of the cursor

(CURROW) - the x coordinate of the cursor

_puts - Puts the text on the screen. This command will bring the specified text to the screen.

_getkey - Detects a key press on the key pad

ld - z80 instruction fo loading something. In this program, it loads 0 (zero) to the "a" register. The syntax is - ld (register), (value#)

Registers

The calculator's memory is where nearly all data is stored. Unfortunately, memory access is relatively slow for the processor. So, when we want the processor to manipulate data, like add two numbers together, we don't want to do it in the memory. Instead, we load the data into special fast memory locations inside the processor itself called registers. In the normal text displaying program (above), the value "0" was saved into the "a" register. The value in the register was then in turn, loaded in to CURCOL and CURROW (the X and Y coordinates of the text). Registers are extremely important! If you don't understand them, I recommend that you read tutorial 4 in Andy S.' tutorials.

Inverse Text

Jeez, things just keep getting better. Inverse text is normal font text (white) on a black backround. This program will display the text "TI-83 Plus Asm" in inverse text. All you need to know to display inverse text is loading text coordinates and setting textinverse mode.

#define bcall(xxxx)	rst 28h \ .dw xxxx		
#define bjump(xxxx)	call 50h \ .dw xxxx	

_clrlcdf		=4540h		
_homeup		=4558h
_puts		=450Ah
CURCOL		=800Dh
CURROW	=800Ch
textinverse	=3			;See the new commands section for more information
textflags		=5	
	
	.org 9D95h	

	bcall(_clrlcdf)	
	bcall(_homeup)
	set	textInverse,(iy+textflags)	;Sets the textinverse mode
	ld	a,0			;Load 0 to the "a" register		
	ld	(CURCOL),a		;Setting Y coordinates
	ld	a,0			;Loading 0 to the "a" register
	ld	(CURROW),a		;Setting X coordinates
	ld	hl,txtTIAsm		;Display text from the TIAsm label		
	bcall(_puts)			;Put text on screen
	res	textInverse,(iy+textflags)	;Resets the text inverse			
	ret				;Return to OS
txtTIAsm:
	.db	" TI-83 Plus Asm ",0	;Text to be displayed on screen
.end
END

New Commands Used

set - z80 instruction that sets the characteristics of the TI

res - z80 instruction which will reset the characteristic

textinverse - Inverse text mode of the TI

textflags - You don't need to know this yet