APEX20KC datasheet(37/90 Pages) ALTERA

37 / 90 page

Altera Corporation

APEX 20KC Programmable Logic Device Data Sheet

Implementing Logic in ROM

In addition to implementing logic with product terms, the ESB can

implement logic functions when it is programmed with a read-only

pattern during configuration, creating a large LUT. With LUTs,

combinatorial functions are implemented by looking up the results, rather

than by computing them. This implementation of combinatorial functions

can be faster than using algorithms implemented in general logic, a

performance advantage that is further enhanced by the fast access times

of ESBs. The large capacity of ESBs enables designers to implement

complex functions in one logic level without the routing delays associated

with linked LEs or distributed RAM blocks. Parameterized functions such

as LPM functions can take advantage of the ESB automatically. Further,

the Quartus II software can implement portions of a design with ESBs

where appropriate.

Programmable Speed/Power Control

APEX 20KC ESBs offer a high-speed mode that supports very fast

operation on an ESB-by-ESB basis. When high speed is not required, this

feature can be turned off to reduce the ESB’s power dissipation by up to

50%. ESBs that run at low power incur a nominal timing delay adder. This

Turbo BitTM option is available for ESBs that implement product-term

logic or memory functions. An ESB that is not used will be powered down

so that it does not consume DC current.

Designers can program each ESB in the APEX 20KC device for either

high-speed or low-power operation. As a result, speed-critical paths in the

design can run at high speed, while the remaining paths operate at

reduced power.

I/O Structure

The APEX 20KC IOE contains a bidirectional I/O buffer and a register

that can be used either as an input register for external data requiring fast

setup times or as an output register for data requiring fast clock-to-output

performance. IOEs can be used as input, output, or bidirectional pins.

APEX20KC датащи(PDF) 37 Page - Altera Corporation