R
Functional Description
Cascading Multipliers
MULT18X18SIO
The MULT18X18SIO primitive has two additional ports
called BCIN and BCOUT to cascade or share the multi-
plier’s ‘B’ input among several multiplier bocks. The 18-bit
BCIN “cascade” input port offers an alternate input source
from the more typical ‘B’ input. The B_INPUT attribute spec-
ifies whether the specific implementation uses the BCIN or
‘B’ input path. Setting B_INPUT to DIRECT chooses the ‘B’
input. Setting B_INPUT to CASCADE selects the alternate
BCIN input. The BREG register then optionally holds the
selected input value, if required.
A[17:0]
B[17:0]
CEA
P[35:0]
CEB
CEP
CLK
RSTA
RSTB
RSTP
BCIN[17:0]
BCOUT is an 18-bit output port that always reflects the
value that is applied to the multiplier’s second input, which is
either the ‘B’ input, the cascaded value from the BCIN input,
or the output of the BREG if it is inserted.
BCOUT[17:0]
DS312-2_28_021205
Figure 37: MULT18X18SIO Primitive
Figure 38 illustrates the four possible configurations using
different settings for the B_INPUT attribute and the BREG
attribute.
BCOUT[17:0]
BCOUT[17:0]
BREG
CE
X
X
CEB
D
Q
BREG = 0
CLK
B_INPUT = CASCADE
RST
BREG = 1
B_INPUT = CASCADE
RSTB
BCIN[17:0]
BCIN[17:0]
BCOUT[17:0]
BCOUT[17:0]
BREG
X
X
CEB
CE
D
B[17:0]
B[17:0]
Q
BREG = 0
B_INPUT = DIRECT
CLK
RST
BREG = 1
B_INPUT = DIRECT
RSTB
DS312-2_29_021505
Figure 38: Four Configurations of the B Input
DS312-2 (v3.8) August 26, 2009
Product Specification
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