Category : C Source Code
Archive   : CUG150.ZIP
Filename : CLINK.ASM

name clink
page 55,132
title 'CLINK - Load and Link Graphics Characters'
assume cs:cseg
;
; CLINK - Load and Link Graphics Character Table
;
; Original by Ray Duncan, published in DDJ #74
; Revised by Patrick Banchy, 1249 Park Ave. #5C, NYC
;
; The IBM PC allows the user to define the meanings of the
; characters in the range 80H-FFH in the graphics modes.
;
; This program when first called will allocate the 1 KB of
; memory needed for the table. Subsequent calls will load
; the table specified in the invocation into memory.
;
fcb equ 05ch ;default file control block
;
eom equ '$' ;literal ending of string
cr equ 13 ;ASCII carriage return
lf equ 10 ;ASCII line feed
;
cseg segment para public 'CODE'
org 100h

clink: ;entry from PC-DOS
xor ax,ax ;see if table has been
mov ds,ax ;previously allocated
mov bx,07ch ;offset of vector
;pick up address of
;table in DS:DX
lds dx,dword ptr [bx]
mov ax,ds
or ax,dx ;have we been here before?
jnz not_1st ;yes,so read the table
;no,set up table
mov ax,cs ;address (restore proper
mov ds,ax ;contents of DS first)
xor dx,dx
mov ah,37 ;using DOS Set Interrupt
mov al,1fh ;call
int 21h
;tell the operator whats up
mov dx,offset nxt_job
mov ah,9
int 21h
;save 1 kbytes for the
mov dx,400h ;table, terminate but
int 27h ;stay resident.

not_1st: ;read in graphics table
mov ah,26 ;first set DTA address
int 21h
mov ax,cs ;restore DS
mov ds,ax
mov dx,offset fcb
mov ah,15 ;try and open file
int 21h
or al,al ;does it exist?
jz file_ok ;yes,proceed
;no,warn operator
mov dx,offset Boo_boo
mov ah,9
int 21h
mov ah,0 ;return to PC-DOS
int 21h

file_ok: ;file exists,read table
mov bx,offset fcb
;set record size = 1024
mov word ptr 14 [bx],400h
;set current rec=zero
mov byte ptr 32 [bx],0
mov dx,offset fcb
mov ah,20 ;sequential read
int 21h
mov dx,offset loaded
mov ah,9 ;tell operator load
int 21h ;was successful

mov ah,0 ;and return to PC-DOS
int 21h

;
; messages for console
;
Boo_boo db cr,lf,'No such file',cr,lf,eom
Loaded db cr,lf,'Character table loaded',cr,lf,eom
Nxt_job db cr,lf,'Memory and Link for table initialized,'
db cr,lf,'Rerun to load the table',cr,lf,lf,eom

cseg ends

end clink

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