ATF1502AS datasheet(3/18 Pages) ATMEL

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ATF1502AS

Each macrocell also generates a foldback logic term, which

goes to a regional bus. Cascade logic between macrocells

in the ATF1502AS allows fast, efficient generation of com-

plex logic functions. The ATF1502AS contains four such

logic chains, each capable of creating sum term logic with a

fan in of up to 40 product terms.

The ATF1502AS macrocell shown in Figure 1, is flexible

enough to support highly complex logic functions operating

at high speed. The macrocell consists of five sections:

product terms and product term select multiplexer;

OR/XOR/CASCADE logic; a flip-flop; output select and

enable; and logic array inputs.

Unused product terms are automatically disabled by the

compiler to decrease power consumption. A Security Fuse,

w hen p r o g r ammed , pr ot ects t he cont ent s of t h e

ATF1502AS. Two bytes (16-bits) of User Signature are

accessible to the user for purposes such as storing project

name, part number, revision or date. The User Signature is

accessible regardless of the state of the Security Fuse.

The ATF1502AS device is an In-System Programmable

(ISP) device. It uses the industry standard 4-pin JTAG

interface (IEEE Std. 1149.1), and is fully compliant with

JTAG’s Boundary Scan Description Language (BSDL). ISP

allows the device to be programmed without removing it

from the printed circuit board. In addition to simplifying the

manufacturing flow, ISP also allows design modifications to

be made in the field via software.

Figure 1. ATF1502AS Macrocell

Product Terms and Select MUX

Each ATF1502AS macrocell has five product terms. Each

product term receives as its inputs all signals from both the

global bus and regional bus.

The product term select multiplexer (PTMUX) allocates the

five product terms as needed to the macrocell logic gates

and control signals. The PTMUX programming is deter-

mined by the design compiler, which selects the optimum

macrocell configuration.

OR/XOR/CASCADE Logic

The ATF1502AS’s logic structure is designed to efficiently

support all types of logic. Within a single macrocell, all the

product terms can be routed to the OR gate, creating a 5-

input AND/OR sum term. With the addition of the CASIN

from neighboring macrocells, this can be expanded to as

many as 40 product terms with a very small additional

delay.

The macrocell’s XOR gate allows efficient implementation

of compare and arithmetic functions. One input to the XOR

comes from the OR sum term. The other XOR input can be

a product term or a fixed high or low level. For combinato-

rial outputs, the fixed level input allows polarity selection.

For registered functions, the fixed levels allow DeMorgan

minimization of product terms. The XOR gate is also used

to emulate T- and JK-type flip-flops.

Flip Flop

The ATF1502AS’s flip flop has very flexible data and con-

trol functions. The data input can come from either the XOR

gate, from a separate product term or directly from the I/O

pin. Selecting the separate product term allows creation of

a buried registered feedback within a combinatorial output

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