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CONTRIBUTIONS/cpm-handbook/cpmsrc/FIG5-14.ASM

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+; Figure 5-14
+;
+;	CCPM
+;	Check if CP/M
+;	This subroutine determines the version number of the
+;	Operating System and, if not CP/M version 2, displays
+;	an error message and executes a warm boot.
+;
+;	Entry and Exit Parameters
+;
+;		None
+;
+;	Calling sequence
+;
+;		CALL	CCPM	;Warm boots if not CP/M 2
+;
+B$PRINTS	EQU	9	;Display $-terminated string
+B$GETVER	EQU	12	;Get version number
+BDOS		EQU	5	;BDOS Entry Point
+;
+CR		EQU	0DH	;Carriage Return
+LF		EQU	0AH	;Line Feed
+;
+CCPMM:	DB	CR,LF
+	DB	'This program can only run under CP/M version 2.'
+	DB	CR,LF,'$'
+;
+;
+CCPM:
+	MVI	C,B$GETVER	;Get version number
+	CALL	BDOS
+	MOV	A,H		;H must be 0 for CP/M
+	ORA	A
+	JNZ	CCPME		;Must be MP/M
+	MOV	A,L		;L = version number of CP/M
+	ANI	0F0H		;Version number in MS Nibble
+	CPI	20H		;Check if version 2
+	JNZ	CCPME		;Must be an earlier version
+	RET			;Yes, we under CP/M version 2
+;
+CCPME:				;Error
+	MVI	C,B$PRINTS	;Display error message
+	LXI	D,CCPMM
+	CALL	BDOS
+	JMP	0		;Warm Boot
+