5

ATF1508AS(L)

0784P–PLD–7/05

Flip-flop

The ATF1508AS’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 output macrocell. (This feature is automatically implemented by the fitter soft-

ware). 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 either the Global CLK Signal (GCK) 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 product

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

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

Extra Feedback

The ATF15xxSE Family macrocell output can be selected as registered or combinatorial. The

extra buried 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 cre-

ation of a second latch within a macrocell.

I/O Control

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

vidually configured as an input, output or for bi-directional operation. The output enable for

each macrocell can be selected from the true or compliment 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, all macrocell resources are still

available, including the buried feedback, expander and cascade logic.

Global Bus/Switch

Matrix

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

all 128 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.

Foldback Bus

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

and is available to 16 macrocells. The foldback is an inverse polarity of one of the macrocell’s

product terms. The 16 foldback terms in each region allows generation of high fan-in sum

terms (up to 21 product terms) with a little additional delay.

3.3V or 5.0V I/O

Operation

The ATF1508AS device has two sets of V

always be connected to a 5.0V power supply. V

patible” with both 3.3V and 5.0V inputs. V

connected for 3.3/5.0V power supply.

Open-collector

Output Option

This option enables the device output to provide control signals such as an interrupt that can

be asserted by any of the several devices.