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CY_MUX

2-to-1 Multiplexer for Carry Logic

XC3000
XC4000E
XC4000X
XC5200
XC9000
Spartan
SpartanXL
Virtex
N/A
N/A
N/A
Primitive
N/A
N/A
N/A
N/A

figures/x4923n.gif

CY_MUX is used to implement a 1-bit high-speed carry propagate function. One such function can be implemented per logic cell (LC), for a total of 4-bits per configurable logic block (CLB). The direct input (DI) of an LC is connected to the DI input of the CY_MUX. The carry in (CI) input of an LC is connected to the CI input of the CY_MUX. The select input (S) of the CY_MUX is driven by the output of the lookup table (LUT) and configured as an XOR function. The carry out (CO) of the CY_MUX reflects the state of the selected input and implements the carry out function of each LC. When Low, S selects DI; when High, S selects CI.

Inputs
Outputs
S
DI
CI
CO
0
1
X
1
0
0
X
0
1
X
1
1
1
X
0
0

The following figure depicts the application of the CY_MUX for a 4-bit adder. Also shown are the associated FMAP symbols and the CY_INIT function.

Figure 4.53 CY_MUX 4-Bit Adder Schematic XC5200

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