XC3S100E Datasheet, PDF (44/193 Pages) Xilinx, Inc – DC and Switching Characteristics

R
Functional Description
The BCIN and BCOUT ports have associated dedicated
routing that connects adjacent multipliers within the same
column. Via the cascade connection, the BCOUT port of
one multiplier block drives the BCIN port of the multiplier
block directly above it. There is no connection to the BCIN
port of the bottom-most multiplier block in a column or a
connection from the BCOUT port of the top-most block in a
column. As an example, Figure 36 shows the multiplier cas-
cade capability within the XC3S100E FPGA, which has a
single column of multiplier, four blocks tall. For clarity, the
figure omits the register control inputs.
BCOUT
A
P
B
B_INPUT = CASCADE
BCIN
BCOUT
A
P
B
B_INPUT = CASCADE
BCIN
BCOUT
A
P
B
B_INPUT = CASCADE
BCIN
BCOUT
A
P
B
B_INPUT = DIRECT
BCIN
DS312-2_30_021505
Figure 36: Multiplier Cascade Connection
When using the BREG register, the cascade connection
forms a shift register structure typically used in DSP algo-
rithms such as direct-form FIR filters. When the BREG reg-
ister is omitted, the cascade structure essentially feeds the
same input value to more than one multiplier. This parallel
connection serves to create wide-input multipliers, imple-
ment transpose FIR filters, and is used in any application
that requires that several multipliers have the same input
value.
DS312-2 (v1.1) March 21, 2005
www.xilinx.com
37
Advance Product Specification