etisserant@0: FUNCTION_BLOCK STACK_INT
etisserant@0:   VAR_INPUT PUSH, POP: BOOL R_EDGE; (* Basic stack operations *)
etisserant@0:             R1 : BOOL ;          (* Over-riding reset *)
etisserant@0:             IN : INT ;           (* Input to be pushed *)
etisserant@0:             N  : INT ;           (* Maximum depth after reset *)
etisserant@0:   END_VAR
etisserant@0:   VAR_OUTPUT EMPTY : BOOL := 1 ;     (* Stack empty *)
etisserant@0:              OFLO  : BOOL := 0 ;     (* Stack overflow *)
etisserant@0:              OUT   : INT  := 0 ;     (* Top of stack data *)
etisserant@0:   END_VAR
etisserant@0:   VAR STK : ARRAY[0..127] OF INT; (* Internal stack *)
etisserant@0:       NI : INT :=128  ;           (* Storage for N upon reset *)
etisserant@0:       PTR : INT := -1 ;           (* Stack pointer *)
etisserant@0:   END_VAR
etisserant@0:     (* Function Block body *)
etisserant@0: 	LD	R1	(* Dispatch on operations *)
etisserant@0: 	JMPC	RESET	
etisserant@0: 	LD	POP	
etisserant@0: 	ANDN	EMPTY	(* Don't pop empty stack *)
etisserant@0: 	JMPC	POP_STK	
etisserant@0: 	LD	PUSH	
etisserant@0: 	ANDN	OFLO	(* Don't push overflowed stack *)
etisserant@0: 	JMPC	PUSH_STK	
etisserant@0: 	RET		(* Return if no operations active *)
etisserant@0: RESET:	LD	0	(* Stack reset operations *)
etisserant@0: 	ST	OFLO	
etisserant@0: 	LD	1	
etisserant@0: 	ST   	EMPTY	
etisserant@0: 	LD	-1	
etisserant@0: 	ST 	PTR	
etisserant@0: 	CAL	LIMIT(MN:=1,IN:=N,MX:=128)
etisserant@0: 	ST	NI	
etisserant@0: 	JMP	ZRO_OUT	
etisserant@0: POP_STK:	LD	0	
etisserant@0: 	ST	OFLO	(* Popped stack is not overflowing *)
etisserant@0: 	LD	PTR	
etisserant@0: 	SUB	1	
etisserant@0: 	ST	PTR	
etisserant@0: 	LT	0	(* Empty when PTR < 0 *)
etisserant@0: 	ST	EMPTY	
etisserant@0: 	JMPC	ZRO_OUT	
etisserant@0: 	LD	STK[PTR]	
etisserant@0: 	JMP	SET_OUT	
etisserant@0: PUSH_STK:	LD	0	
etisserant@0: 	ST	EMPTY	(* Pushed stack is not empty *)
etisserant@0: 	LD	PTR	
etisserant@0: 	ADD	1	
etisserant@0: 	ST	PTR	
etisserant@0: 	EQ	NI	(* Overflow when PTR = NI *)
etisserant@0: 	ST	OFLO	
etisserant@0: 	JMPC	ZRO_OUT	
etisserant@0: 	LD	IN	
etisserant@0: 	ST	STK[PTR]	(* Push IN onto STK *)
etisserant@0: 	JMP	SET_OUT	
etisserant@0: ZRO_OUT:	LD	0	(* OUT=0 for EMPTY or OFLO *)
etisserant@0: SET_OUT:	ST 	OUT	
etisserant@0: 
etisserant@0:   END_FUNCTION_BLOCK