🚀 go-pugleaf

Hello,
  I am very new to assembly language and I have a question.  I am
trying to write a tsr that will write characters typed from they
keyboard into a file.  I have been making my attempts by using
a tsr skeleton provided in Peter Norton's Assembler book.  I have
been able to read the keystrokes and display them on a different
section of screen,make a speaker beeping noise after each keystroke
etc.  My problem is when I try to write the characters to a file.
I can open a file, but after about 5 or 6 keystrokes my system
freezes up.  I have tried all sorts of methods of writing the
characters with no luck.  I have enclosed the basic tsr skeleton
below.  It will open a file, set up the keyboard interrupt vector,
and launch the tsr section of the code.  Could someone help
me in figuring out how to write the characters to a file using
the skeleton of code below?  I could really use the help!!!
Thanks!
Jim
buckley@milton.u.washington.edu


--------------------------CODE STARTS HERE--------------------------------
INTERRUPT_NUMBER        EQU     9
	.MODEL SMALL

ROM_BIOS_DATA   SEGMENT AT 40H   ;keyboard buffer here
	ORG     1AH
	HEAD    DW      ?	 ;unread characters go from Head to Tail
	TAIL    DW      ?
	BUFFER  DW      16 DUP (?)
	BUFFER_END      LABEL   WORD
ROM_BIOS_DATA   ENDS

	.CODE
	ORG     100H
FIRST:  JMP     LOAD_PROG


	OLD_KEY_INT     LABEL   WORD
	OLD_KEYBOARD_INT        DD      ?	;location of old keybd intrpt
	FILE    DB      "D:\ABC.DAT",0		;test file name to write to
	HANDLE  DW	0			;file handle


PROG    PROC
	PUSH    AX
	PUSH    BX
	PUSH    CX
	PUSH    DX
	PUSH    DI
	PUSH    SI
	PUSH    DS
	PUSH    ES
	PUSHF
	CALL    OLD_KEYBOARD_INT

;get character typed
	ASSUME DS:ROM_BIOS_DATA
	MOV     BX,ROM_BIOS_DATA
	MOV     DS,BX
	MOV     BX,TAIL
	CMP     BX,HEAD
	JE      EXIT
	SUB     BX,2
	CMP     BX,OFFSET BUFFER
	JAE     NO_WRAP
	MOV     BX,OFFSET BUFFER_END
	SUB     BX,2
NO_WRAP: MOV    DX,[BX]  ;dx contains character typed

; NEW CODE GOES HERE --


;say an alt-s  (a DX of 1F00)  closes file

	CMP 	DX,1F00H
	JNE	WRITE
	;code to close file goes here
	JMP	EXIT
	
WRITE:
	;code to write characters to file

;end of new code--restore registers
EXIT:   POP     ES
	POP     DS
	POP     SI
	POP     DI
	POP     DX
	POP     CX
	POP     BX
	POP     AX
	IRET
PROG    ENDP


;initialize everything/open file (not part of tsr)
LOAD_PROG       PROC
	
	;OPEN FILE--ASSUME IT ALREADY EXISTS FOR NOW
	MOV     DX,OFFSET FILE
	MOV     AX,3D02H
	INT     21H
	MOV     HANDLE,AX


	;save old intrpt vector
	MOV     AH,35H		
	MOV     AL,INTERRUPT_NUMBER
	INT     21H
	MOV     OLD_KEY_INT,BX
	MOV     OLD_KEY_INT[2],ES
	;set new interrupt vecotr
	MOV     AH,25H
	LEA     DX,PROG
	INT     21H
	MOV     DX,OFFSET LOAD_PROG
	INT     27H
LOAD_PROG       ENDP
END     FIRST
--------------------------------CODE ENDS HERE--------------------------------