參數(shù)資料
型號: XC5000
廠商: Xilinx, Inc.
英文描述: Logic Cell Array Family
中文描述: 邏輯單元陣列系列
文件頁數(shù): 13/48頁
文件大?。?/td> 434K
代理商: XC5000
R
9
Carry Function
The XC5200 family supports a carry-logic feature that
enhances the performance of arithmetic functions such as
counters, adders, etc. A carry multiplexer (CY_MUX)
symbol on a schematic is used to indicate the XC5200
carry logic. This symbol represents the dedicated 2:1
multiplexer in each LC that performs the one-bit high-
speed carry propagate per logic cell (four bits per CLB).
While the carry propagate is performed inside the LC, an
adjacent LC must be used to complete the arithmetic
function. Figure 6 represents an example of an adder
function. The carry propagate is performed on the CLB
shown, which also generates the half-sum for the four-bit
adder. An adjacent CLB is responsible for XORing the
half-sum with the corresponding carry-out. Thus an adder
or counter requires two LCs per bit. Notice that the carry
chain requires an initialization stage, which the XC5200
family accomplishes using the carry initialize (CY_INIT)
macro and one additional LC.
The XC5200 library contains a set of RPMs and arithmetic
functions designed to take advantage of the dedicated
carry logic. Using and modifying these macros makes it
much easier to implement customized RPMs, freeing the
designer from the need to become an expert on
architectures.
Figure 6.
XC5200 CY_MUX Used for Adder Carry Propagate
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
XOR
XOR
XOR
XOR
F=0
DI
DI
DI
DI
FD
FD
FD
FD
carry out
carry3
DO
D
X
LC3
DO
D
Q
LC2
DO
X
CI
carry in
CY_MUX
CY_MUX
CY_MUX
CY_MUX
CY_MUX
X
DO
DO
Q
DO
LC1
LC0
CK
CE
CLR
D
D
Q
Q
X
Q
half sum0
carry0
half sum2
half sum1
carry1
carry2
half sum3
CO
A3
or
B3
A3 and B3
to any two
A2 and B2
to any two
A2
or
B2
A1
or
B1
A1 and B1
to any two
A0
or
B0
A0 and B0
to any two
0
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
XOR
XOR
XOR
XOR
DI
DI
DI
DI
FD
FD
DO
FD
FD
D
X
LC3
DO
D
Q
LC2
X
CI
X
LC1
LC0
CK
CE
CLR
D
D
Q
X
Q
sum0
sum2
sum1
sum3
CO
Initialization of
carry chain (One Logic Cell)
X5709
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