Ports

Port Name	Type	Usage	Description	Comments
DataA	I	Required	Augend/Minuend	Vector, LPM_Width wide
DataB	I	Required	Addend/Subtrahend	Vector, LPM_Width wide
Cin	I	Optional	Carry in to the low order bit OP=ADD Low= 0 High= +1 OP=SUB Low = -1 High= 0	If not connected, default value is LOW.
Add_Sub	I	Optional	The Operation to be performed =H: OP = ADD =L: OP = SUB	Cannot be used it LPM_Direction property is used. If not connected, defaults value is ADD.
Result	O	Required	DataA ± DataB ± Cin	Vector, LPM_Width wide
Cout	O	Optional	Carry-out (~Borrow-in) of Most Significant Bit (MSB)	Note 1
Overflow	O	Optional	Result exceeds available precision.	Note 2
Clock	I	Optional	Clock for pipelined usage	Note 3
Aclr	I	Optional	Asynchronous Clear	Note 4

Note 1: Cout has a physical interpretation as the carry-out (~borrow-in) of the most significant bit. Cout is most meaningful for detecting overflow in unsigned numbers. See Table 1 for the arithmetic interpretation of Cout = 1.

Note 2: Overflow has a physical interpretation as the XOR (exclusive or) of the carry into the MSB with the carry out of the MSB. Overflow is only meaningful when the LPM_Representation is signed. It indicates that the Result has exceeded the available precision. See Table 2 for the arithmetic interpretation of Overflow = 1.

Note 3: The clock port provides for pipelined operation of the LPM_ADD_SUB. If a latency other 0 (default value) is specified, then the clock port must be connected.

Note 4: The pipelined initializes to undefined. The Aclr port may be used at any time to reset the pipeline to all 0's asynchronously to clock.

Table 1	OP = ADD	OP = SUB
Unsigned	(DataA + DataB + Cin) > 2LPM_Width-1	Normal Subtract. However, if Cout = 0, then (DataA - DataB - Cin) < 0
Signed	Normal result of adding two negative numbers, or possible overflow.	Normal result when subtracting a positive number from a negative number, or possible overflow.

Table 2	OP=ADD	OP=SUB
Unsigned	Not meaningful	Not meaningful
Signed	(DataA + DataB + Cin) > 2LPM_Width-1-1 or (DataA + DataB + Cin) < -2LPM_Width-1	(DataA - DataB - Cin) > 2LPM_Width-1-1 or (DataA - DataB - Cin) < -2LPM_Width-1

Properties

Property	Usage	Value	Comments
LPM_Width	Required	LPM Value > 0	Width of DataA, DataB and Result
LPM_Direction	Optional	ADD | SUB	Default is ADD. Add_Sub port may not be used if this property is used.
LPM_Representation	Optional	UNSIGNED or SIGNED	Default is SIGNED
LPM_Pipeline	Optional	LPM Value > = 0	Default is 0 - non-pipelined

Functions

Resulti = DataAi ^ DataBi ^ Cini ^ (~ Add_Sub)

Cout = carry out of the MSB

Overflow = the XOR of the carry into the MSB and Cout

When Cout is prepended to the Result, the result is a vector that always has sufficient precision to represent the result of the operation.

{Cout,Result} = DataA + Cin ± DataB

Copyright © 1998 University of Manchester