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Function Description
The PEEL™22CV10A implements logic functions as sum-
of-products expressions in a programmable-AND/ fixed-OR
logic array. User-defined functions are created by program-
ming the connections of input signals into the array. User-
configur able o utput str uctu res in the fo rm of I/O ma croc ells
further incr eas e log ic flex ibili ty.
Architecture O verview
The PEEL™22CV10A architecture is illustrated in the block
diagram of Figure 2. Twelve dedicated inputs and 10 I/Os
provid e up to 22 inp uts and 10 o utputs for cr eation of logic
functions. At the core of the device is a programmable elec-
trically-erasable AND array which drives a fixed OR array.
With this structure, the PEEL™22CV10A can implement up
to 10 sum-of-products logic expressions.
Associated with each of the 10 OR functions is an I/O mac-
rocell which can be in depend ently programm ed to one of 4
different configurations. The programmable macrocells
allow each I/O to create sequential or combinatorial logic
functions with either active-high or active-low polarity.
AND/OR Logic Array
The programmable AND array of the PEEL™22CV10A
(shown in Figure 3) is formed by input lines intersecting
product terms. The in put lines a nd product ter ms are used
as follows:
44 Input Lines:
24 input lines carry the true and complement
of the signals applied to the 12 input pins
20 additional lines carry the true and complement
values of feedback or input signals from
the 10 I/Os
132 product terms:
120 product terms (arranged in 2 groups of 8,
10, 12, 14 and 16) used to form logical sums
10 output enable terms (one for each I/O)
1 global synchronous present term
1 global asynchronous clear term
At each input-line/product-term intersection there is an
EEPROM memory cell which determines whether or not
there is a logical connection at that intersection. Each prod-
uct term is es se nti all y a 44- input AND gate . A p r oduct term
which is c onnected to b oth the true and complement of an
input signal will always be FALSE, and thus will not affect
the OR fu nction th at it drive s. When al l the con nections o n
a product term are opened, a “don’t care” state exists and
that term will always be TRUE. When programming the
PEEL™22CV10A, the device programmer first performs a
bulk erase to remove the previous pattern. The erase cycle
opens every logical connection in the array. The device is
then configured to perform the user-defined function by
programming selected connections in the AND array. (Note
that PEEL™ device programmers automatically program
the connections on unused product terms so that they will
have no effect on the output function.)
Variable Product Term Distribution
The PEEL™ 22CV10A provi des 120 product ter ms to drive
the 10 OR functions. These product terms are distributed
among the outputs in groups of 8, 10, 12, 14 and 16 to form
logical sums (see Figure 3). This distribution allows opti-
mum use of device re-sources.
Programmable I/O Ma croce ll
The output macrocell provides complete control over the
architecture of each output. The ability to configure each
output independently permits users to tailor the configura-
tion of the P EE L™2 2CV 10A to the pr ecis e r eq uirem ents of
their designs.
Macrocell Architecture
Each I/O macroc ell, as shown in Figure 4, consists of a D-
type flip-flop and two signal-select multiplexers. The config-
uration of each macrocell is determined by the two
EEPROM bits contr olling these mu ltiplexers (refe r to Table
1). These bits determine output polarity and output type
(registered or non-registered). Equivalent circuits for the
four macro-cell configurations are illustrated in Figure 5.
Output Type
The sign al from the OR ar ra y ca n be fed di rect ly to the out-
put pin (combinatorial function) or latched in the D-type flip-
flop (registered function). The D-type flip-flop latches data
on the r ising e dge of the clock a nd is cont rolled by the glo-
bal preset and clear terms. When the synchronous preset
term is satisfied, the Q output of the register will be set
HIGH at the next rising edge of the clock input. Satisfying
the asyn chronou s clear te rm will set Q LOW, re gardless o f
the clock state. If both terms are satisfied simultaneously,
the clear will override the preset.
Output Polarity
Each macrocell can be configured to implement active-high
or active-low logic. Programmable polarity eliminates the
need for external inverters.
Output Enable
The output of each I/O macrocell can be enabled or dis-
abled under the control of its associated programmable
output enable product term. When the logical conditions
programmed on the output enable term are satisfied, the
output signal is propagated to the I/O pin. Otherwise, the
output buffer is driven into the high-impedance state.
Under the control of the output enable term, the I/O pin can
function as a dedicated input, a dedicated output, or a bi-
directional I/O. Opening every connection on the output