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3492A–PLD–12/05

ATF1502BE

1.3

Flip-flop

The ATF1502BE’s flip-flop has very flexible data and control 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 out-

put macrocell. (This feature is automatically implemented by the fitter software). In addition to D,

T, JK and SR operation, the flip-flop can also be configured as a flow-through latch. In this

mode, data passes through when the clock is high and is latched when the clock is low.

The clock itself can be any one of the Global CLK signals (GCK[0 : 2]) or an individual product

term. The flip-flop changes state on the clock’s rising edge. When the GCK signal is used as the

clock, one of the macrocell product terms can be selected as a clock enable. When the clock

enable function is active and the enable signal (product term) is low, all clock edges are ignored.

The flip-flop’s asynchronous reset signal (AR) can be either the Global Clear (GCLEAR), a prod-

uct term, or always off. AR can also be a logic OR of GCLEAR with a product term. The

asynchronous preset (AP) can be a product term or always off.

1.4

Extra Feedback

The ATF1502BE macrocell output can be selected as registered or combinatorial. The extra bur-

ied feedback signal can be either combinatorial or a registered signal regardless of whether the

output is combinatorial or registered. (This enhancement function is automatically implemented

by the fitter software.) Feedback of a buried combinatorial output allows the creation of a second

latch within a macrocell.

1.5

I/O Control

The output enable multiplexer (MOE) controls the output enable signal. Each I/O can be individ-

ually configured as an input, output or bi-directional pin. The output enable for each macrocell

can be selected from the true or complement of the two output enable pins, a subset of the I/O

pins, or a subset of the I/O macrocells. This selection is automatically done by the fitter software

when the I/O is configured as an input or bi-directional pin.

1.6

Global Bus/Switch Matrix

The global bus contains all input and I/O pin signals as well as the buried feedback signal from

all 32 macrocells. The switch matrix in each logic block receives as its inputs all signals from the

global bus. Under software control, up to 40 of these signals can be selected as inputs to the

logic block.

1.7

Foldback Bus

Each macrocell also generates a foldback product term. This signal goes to the regional bus and

is available to all 16 macrocells within the logic block. The foldback is an inverse polarity of one

of the macrocell’s product terms. The 16 foldback terms in each logic block allow generation of

high fan-in sum terms or other complex logic functions with little additional delay.