The Programmer's Guide to TRSDOS Version 6 - Tim Mann's Home ...

8.15 SLASH0 Filter Illustrated
;SLASH0/FLT - Version 6.0 - 05/27/83
;
COM ''
;
;*=*=*
; This filter will provide slashed zeroes on
; printers capable of accepting a backspace
;*=*=*
;
LF EQU 10
CR EQU 13
@CHNIO EQU 20
@HIGH$ EQU 100
@DSPLY EQU 10
@FLAGS$ EQU 101
@LOGOT EQU 12
ORG 3000H
BEGIN PUSH DE
POP IX ;Get dcb
LD (MODDCB),DE ;Stuff DCB pointer
LD HL,HELLO$
LD A,@DSPLY ;Display hello
RST 40
;*=*=*
; Check if entry from SET command
;*=*=*
LD A,@FLAGS$ ;Get flags pointer
RST 40
BIT 3,(IY+'C'-'A') ;System request?
JP Z,VIASET
;*=*=*
; install new HIGH$ and move filter code
;*=*=*
LD HL,0 ;Get current HIGH$
LD B,L
LD A,@HIGH$
RST 40
JR NZ,NOMEM
LD (OLDHI),HL ;Put in filter header
;*=*=*
; Relocate internal references in driver
;*=*=*
LD IY,RELTAB ;Point to relocation tbl
LD DE,MODEND
OR A ;Clear carry flag
SBC HL,DE
LD B,H ;Move to BC
LD C,L
RLOOP LD L,(IY) ;Get address to change
LD H,(IY+1)
LD A,H
OR L
JR Z,RXEND
LD E,(HL) ;P/U address
INC HL
LD D,(HL)
EX DE,HL ;Offset it
ADD HL,BC
EX DE,HL
LD (HL),D ;And put back
DEC HL
LD (HL),E
INC IY
INC IY
JR RLOOP ;Loop till done
;*=*=*
; Move driver into high memory
;*=*=*
RXEND LD DE,(OLDHI) ;Destination address
LD HL,MODEND ;Last byte of module
LD BC,LENGTH ;Length of filter
LDDR
8-38