ATF1516AS/L
4
Product Terms and Select MUX
Each ATF1516AS macrocell has five product terms. Each
product term recei ve s as i ts inp uts al l s ig nal s f ro m bo th th e
global bus and regional bus.
The product term select multip lexer ( PTMUX ) alloc ates th e
five product terms as needed to the macrocell log ic gates
and control signals. The PTMUX programming is determined by the design c ompiler, which selec ts the opt imum
macrocell configuration.
OR/XOR/CASCADE Logic
The ATF1516AS’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 5input 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 func tions. O ne input to th e XOR
comes from the OR sum term. The other XOR input can be
a product term or a fixed high or low level. For combinatorial outputs, the fi xed level input allow s polarit y selectio n.
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 ATF1516AS’s flip flop has very flexible data and control functions. The data input can come from either the
XOR gate, from a se parate prod uct term or d irectly fr om
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 fit ter so ftware). I n additi on to D , T, J K and
SR operation, the flip flop can also be configured as a flowthrough latch. In this mode, da ta passes th rough whe n the
clock is high and is latched when the clock is low.
The clock itself can eith er be th e Global CLK Si gnal (GC K)
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 f lip flop’s asynchronous re se t
signal (AR) can be either the Global Clear (G CLEAR), a
product term, or always off. A R can also be a logi c OR of
GCLEAR with a product term. The as ynchronous prese t
(AP) can be a product term or always off.
Output Select and Enable
The ATF1516AS macrocell output can be selected as registered or combinatorial. The buried feedback signal can be
either combinatorial or registered signal regardless of
whether the output is combinatorial or registered.
The output enable multiplexer (MOE) controls the output
enable signals. A ny buffer can b e perman ently enab led for
simple output operation. Buffers ca n also be permanently
disabled to allow use of the pin as an i nput. In this confi guration all the macr oce ll res our ces are s till ava ilab le, i ncl uding the buried feedback, expander and CASCADE logic.
The output enable for each macrocell can be selected as
either of the two dedicated OE input pins as an I/O pin configured as an input, or as an individual product term.
Global Bus/Switch Matrix
The global bus contains all input and I/O pin signals as well
as the buried fe edback signal from all 256 macr ocells.
The Switch Matrix in ea ch 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 a lso generate s a foldbac k product ter m.
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 te rms in eac h
region allows generation of hi gh fan -in su m ter ms (up to 21
product terms) with a small additional delay.