6
ATF1504AS(L)
0950N–PLD–07/02
Product Terms and Select
Mux
Each ATF1504AS macrocell has five product terms. Each product term receives as its
possible 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
determined by the design compiler, which selects the optimum macrocell configuration.
OR/XOR/CASCADE Logic The ATF1504AS’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 little 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 combinatorial 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 ATF1504AS’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 feed-
back within a combinatorial output 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 either 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 sig-
nal 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 asynchronous preset (AP) can be a product
term or always off.
Output Select and Enable The ATF1504AS 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. Any buffer can
be permanently enabled for simple output operation. Buffers can also be permanently
disabled to allow use of the pin as an input. In this configuration all the macrocell
resources are still available, including the buried feedback, expander and CASCADE
logic. The output enable for each macrocell can be selected as either of the two dedi-
cated 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 feedback sig-
nal from all 64 macrocells. The switch matrix in each logic block receives as its possible
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.
