Basic Teletype Display Code

The default TTY Teletype font and operation displays light grey characters on the display on a black background.
You must set AX, BX and CX before calling INT 0x10.

Set AH=E0 this is the display command for TTY mode.
Set AL= the character to be displayed. All 256 characters can be used.
Set BX=0x0007 the default colour.
Set CX=0x0001 to the number of characters to display.

You can ignore the PUSH and POP stack commands if you do not mind your registers changing.

Display a Character

; Prints a single character on the display ; Pass AL = character to print ; BL = foreground color (graphics modes only) ; (Defaults to 07) SubDisplayTTYCharacter: PUSH EAX PUSH EBX PUSH ECX MOV CX, 0x0001 MOV BH, 0x07 ; Sets colour (Light Grey for Text mode) MOV AH, 0x0E ; Set the Video Mode (0E write to TTY screen) INT 0x10 POP ECX POP EBX POP EAX RET

Display a String

; Print a NULL terminated string to the display ; Pass ESI = string location SubDisplayTTYString: CLD PUSH EAX PUSH EBX PUSH ECX PUSH ESI MOV CX, 0x0001 ; print one letter MOV BH, 0x07 ; Sets colour (Light Grey for Text mode) LODSB ; Loads AL with the required character one byte at a time CMP AL, 0x00 ; Look for the NULL zero JE 0x06 ; Jump to return MOV AH, 0x0E ; Set the Video Mode (0E write to TTY screen) INT 0x10 JMP 0xF5 ; Repeat for next character POP ESI POP ECX POP EBX POP EAX RET

Display a Number

; Displays the number of the display ; Pass EAX = Number to display SubDisplayTTYNumber: PUSH EAX PUSH EBX PUSH ECX PUSH EDX CLD MOV CX, 0x0000 MOV BX, 0x000A MOV DX, 0x0000 DIV BX ; Divide EAX by EBX=10 PUSH EDX ; Save the Number on the stack INC CX ; Count each number CMP AX, 0x00 ; Check if EAX = NULL JNE 0xF4 ; Jump to Repeat if EAX is not Zero POP EAX ; Retrieve the saved numbers from the stack ADD AL, 0x30 ; Adds 48 to get the ASCII digit CALL SubDisplayTTYCharacter ; Display a character LOOP 0xF8 ; Jump to Repeat if ECX is greater than Zero POP EDX POP ECX POP EBX POP EAX RET

Display a New Line

; Prints a single New Line pair SubDisplayTTYNewLine: PUSH EAX MOV AL, 0x0D CALL SubDisplayTTYCharacter ; Displays Carriage Return MOV AL, 0x0A CALL SubDisplayTTYCharacter ; Display New Line POP EAX RET

Display a HEX Number

The \\0 in the data string represents a NULL (zero) end of string. The data string will need to be modified for use with your own compiler.

; Displays the number passed to the routine as a Hex number. ; Pass EAX = number to be displayed ; Returns Nothing DataHexArray: '0123456789ABCDEF\\0' SubDisplayTTYHexNumber: PUSH EAX PUSH ECX PUSH EDX PUSH EBX PUSH ESI MOV CX, 0x0000 MOV BX, 0x0010 ; 0x10h (16) MOV DX, 0x0000 DIV BX ; Divide EAX by EBX=0x10h PUSH EDX INC CX ; Count each number CMP AX, 0x00 ; Check if EAX = 0 JNE 0xF4 ; Jump to Repeat if EAX is not Zero CLD POP EAX ; Retrieve the saved numbers from the stack MOV SI, DataHexArray ADD SI, AX LODSB CALL SubTTYCharacte LOOP 0xF4 ; Jump to Repeat if ECX is greater than Zero POP ESI POP EBX POP EDX POP ECX POP EAX RET

Display a Press Key Message

The \\0 in the data string represents a NULL (zero) end of string. The data string will need to be modified for use with your own compiler.

; Displays the Press any key message and waits for a reply ; Pass ESI = Source Address ; Reply in AH=Shift, AL=Character DataPressAnyKey: 'Press any key to continue\\0' SubDisplayTTYPressAnyKey: PUSH ESI MOV SI, DataPressAnyKey CALL SubDisplayTTYString MOV AX, 0x0000 ; Get the next character from the keyboard INT 0x16 POP ESI RET

Last Update 27/12/2022