ep1m120 Altera Corporation, ep1m120 Datasheet - Page 24

• Manufacturer Part Number: ep1m120
• Description: Programmable Logic Device Family
• Manufacturer: Altera Corporation

Mercury Programmable Logic Device Family Data Sheet
24
The Quartus II Compiler creates carry chains longer than ten LEs by
linking LABs together automatically. For enhanced fitting, a long carry
chain skips intermediate LABs in a row structure. A carry chain longer
than one LAB skips either from an even-numbered LAB to the next even-
numbered LAB, or from an odd-numbered LAB to the next odd-
numbered LAB. For example, the last LE of the first LAB in a LAB row
carries to the first LE of the third LAB in the same LAB row.
Multiplier Mode
Multiplier mode is used for implementing high-speed multipliers up to
16 16 in size. The LUT implements the partial product formation and
summation in a single stage for a N M-bit multiply operation. A single
LE can implement the summation of A
multiplier and multiplicand inputs. To increase the speed of the
multiplication, LAB wide signals are used to control the partial product
sum generation. These multiplier LAB-wide signals use the LABCLKENA1
and PRESET/ASYNCLOAD resources. The multiplier mode takes
advantage of the CSLA circuitry for optimized sum and carry generation
in the partial product sum. There is a special CSLA circuitry mode used
for the multiplier where the carry chain runs vertically between LABs in
the same column. The Quartus II Compiler automatically uses this special
mode for dedicated multiplier implementation only. The summation of
the multiplier and multiplicand bits is driven out along with the carry-
out0 and carry-out1 bits. The combinatorial or registered versions of
the sum can be driven out, allowing the multiplier to be pipelined.
The RapidLAB interconnect has dedicated fast connections to the LE
inputs in multiplier mode, further increasing the speed of the multiplier.
These dedicated connections allow RapidLAB lines to avoid delay
incurred by driving onto local interconnects and then into the LE.
The Quartus II software implements parameterized functions that use the
multiplier mode automatically when multiply operators are used.
Figure 11
shows a Mercury device LE in multiplier mode.
N
B
M + 1
+ A
N + 1
B
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