; TITLE		4-bit 2's Complimentor 								;

CHIP    2COMP  NFX780_84		; Is this the right chip ??? 

; INPUTS 

PIN     [47:50] 	a[0:3]  	      ; the 4 bit number to be 2's complemented 


; OUTPUTS 
                       		 	;  +---s6---+
PIN     34      s0  	  	   	;  |        |
PIN     35      s1     			; s5        s4
PIN     36      s2      		;  |        |
PIN     37      s3      		;  +---s3---+
PIN     39      s4      		;  |        |
PIN     40      s5      		; s2        s1
PIN     41      s6      		;  |        |
                        		;  +---s0---+

PIN     cp[0:3]  		  	 	; the 2's complement of a[0:3]
PIN     cout                   	; dump the carry output here
PIN     inv[0:3]                	; the inversion of a[0:3] will be stored on these nodes

; UNUSED PINS 


PIN	  [51]	unused0
PIN	  [77:78] 	unused[1:2]
					  	

EQUATIONS
	inv[0:3]=/a[0:3]	; inverts all 4 inputs 	


; Perform the 2's complement: invert the input and add 1  

MODULE add4 FILE 4bfuladd ( a[0:3]=inv[0:3], b0=VCC, b1=GND, b2=GND, b3=GND, cin=GND, sum[0:3]=cp[0:3], cout=cout )


; Decode the 2's complement and output it to the 7-segment display 

T_TAB ( cp3 cp2 cp1 cp0 >> s0 s1 s2 s3 s4 s5 s6 )
        0  0  0  0  :  1  1  1  0  1  1  1  ;  0  
        0  0  0  1  :  0  1  0  0  1  0  0  ;  1
        0  0  1  0  :  1  0  1  1  1  0  1  ;  2
        0  0  1  1  :  1  1  0  1  1  0  1  ;  3
        0  1  0  0  :  0  1  0  1  1  1  0  ;  4
        0  1  0  1  :  1  1  0  1  0  1  1  ;  5
        0  1  1  0  :  1  1  1  1  0  1  1  ;  6
        0  1  1  1  :  0  1  0  0  1  0  1  ;  7
        1  0  0  0  :  1  1  1  1  1  1  1  ;  8
        1  0  0  1  :  1  1  0  1  1  1  1  ;  9
        1  0  1  0  :  0  1  1  1  1  1  1  ;  A
        1  0  1  1  :  1  1  1  1  0  1  0  ;  b
        1  1  0  0  :  1  0  1  0  0  1  1  ;  C
        1  1  0  1  :  1  1  1  1  1  0  0  ;  d
        1  1  1  0  :  1  0  1  1  0  1  1  ;  E
        1  1  1  1  :  0  0  1  1  0  1  1  ;  F


; SIMULATION: Run through all 16 possible inputs and spit out it's 2's complement
; expected output: Should effectively count down from F - 0				    

SIMULATION

	VECTOR in_a := [  a3,  a2,  a1,  a0 ]
	VECTOR comp := [ cp3, cp2, cp1, cp0 ]
	VECTOR seg_display := [s0, s1, s2, s3, s4, s5, s6]

	TRACE_ON in_a comp seg_display

        FOR i:=0 TO 15 DO
		BEGIN
		SETF in_a := i
		END