EP1M350 datasheet(24/86 Pages) ALTERA

24 / 86 page

Altera Corporation

Mercury Programmable Logic Device Family Data Sheet

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 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 ANBM + 1 + AN + 1BM for the

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.

EP1M350 Datasheet(PDF) 24 Page - Altera Corporation