xc5210 Xilinx Corp., xc5210 Datasheet - Page 13

• Manufacturer Part Number: xc5210
• Description: Logic Cell Array Family , Inc
• Manufacturer: Xilinx Corp.

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
Figure 6.
A1 and B1
to any two
0
A0
or
B0
A0 and B0
to any two
A3
or
B3
A3 and B3
to any two
A2
or
B2
A2 and B2
to any two
A1
or
B1
XC5200 CY_MUX Used for Adder Carry Propagate
F=0
DI
DI
DI
DI
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
XOR
XOR
XOR
XOR
CI
CY_MUX
CO
carry in
CY_MUX
CY_MUX
CY_MUX
CY_MUX
Initialization of
carry chain (One Logic Cell)
carry out
CE
CK
CLR
D
D
D
D
FD
FD
FD
FD
LC3
LC2
LC1
LC0
DO
DO
DO
DO
Q
Q
X
Q
X
X
X
Q
half sum3
carry2
half sum2
carry1
half sum1
carry0
half sum0
carry3
9
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.
DI
DI
DI
DI
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
F4
F3
F2
F1
XOR
XOR
XOR
XOR
CI
CO
CE
CK
CLR
D
D
D
D
FD
FD
FD
FD
LC3
LC2
LC1
LC0
DO
DO
DO
DO
Q
Q
X
X
Q
X
X
Q
sum3
sum2
sum1
sum0
X5709
R