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CPM OPERATING SYSTEMS/CPM 3.X/CPM 3.0/SOURCE/echovers.asm

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+	; ECHOVERS RSX
+
+pstring	equ	9			; string print function
+cr	equ	0dh
+lf	equ	0ah
+;
+;		RSX PREFIX STRUCTURE
+;
+	db	0,0,0,0,0,0		; room for serial number
+	jmp	ftest			; begin of program
+next	db	0c3H			; jump
+        dw	0			; next module in line
+prev:	dw	0			; previous module
+remov:	db	0ffh			; remove flag set
+nonbnk:	db	0
+	db	'ECHOVERS'
+space:	ds	3
+
+ftest:					; is this function 12?
+	mov 	a,c 
+	cpi 	12 
+	jz 	begin			; yes - intercept
+        jmp 	next			; some other function 
+
+begin:
+	lxi 	h,0	
+	dad 	sp 			;save stack
+	shld 	ret$stack
+	lxi 	sp,loc$stack
+
+	mvi 	c,pstring 
+	lxi 	d,test$msg		; print message
+	call 	next			; call BDOS
+
+	lhld 	ret$stack 		; restore user stack
+	sphl
+	lxi 	h,0031h			; return version number = 0031h
+	ret
+
+test$msg:
+	db	cr,lf,'**** ECHOVERS **** $'
+ret$stack:	
+	dw	0
+	ds	32			; 16 level stack
+loc$stack:
+	end