Anachip Corp.
www.anachip.com.tw Rev. 1.0 Dec 16, 2004
3/10
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-
configurable output structures in the form of I/O macrocells
further increase logic
flexibility.
Architecture Overview
The
PEEL™22CV10A
architecture is illustrated in
the block
diagram of
Figure 2.
Twelve dedicated
inputs and 10 I/Os
provide up to 22 inputs and 10 outputs for creation 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 independently
programmed 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 input lines and product terms 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 essentially a 44-input AND gate. A product term
which is connected to both the true
and
complement
of an
input
signal will always be
FALSE, and thus will
not
affect the
OR function that it drives. When
all the connections on 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 provides 120 product terms 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 Macrocell
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 PEEL™22CV10A to
the
precise requirements of
their designs.
Macrocell Architecture
Each I/O
macrocell,
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 controlling these multiplexers (refer 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 signal from the
OR array can be fed directly
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 rising edge of the clock and
is controlled
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
asynchronous clear term will set Q LOW, regardless of 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