
F igure 4. Cell Structure
(continued)
the array with read/write access to two North-South and
two East -West buses.
Each cell, in addit ion, provid es t he abilit y to rout e a sig nal
on a 90° turn between the NS1 bus and EW1 bus and
between the NS 2 bus and EW2 bus.
Express buses are not connected directly to cells, and
thus provide higher speeds. They are the fastest way to
cover long, straight-l ine distances within the ar ray.
Each exp ress bus is paired wi th a local bus, so there ar e
two express buses for every column and two express
buses for every row of cells.
Connective units, called repeaters, spaced every eight
cells, divide each bus, both local and express, into seg-
m ents spanning eight cells. Repeat ers are aligned i n rows
and columns thereby p artitioning the ar ray into 8 x 8 sec-
tors of cells. Each repeater is associated with a local/ex-
press pair, and on each side of the repeater are connec-
tions to a local-bus segment and an express-bus segment.
The repeater can be prog rammed to provide any one of
twenty-one connecting functions. These functions are
sym metric wi th respect t o bot h the tw o repeater sides and
the two t y pes of buses.
Among the functions provi ded are the abi lit y to:
•Isol ate bus segment s from one another
•C onnect two local-bus segme nts
•C onnect two express-bus segme nts
•Imp lement a local/express transf er
In al l of these cases, each connect ion provid es signal re-
generation and is thus unidirectional. For bidirectional
connections, t he basi c repeater f uncti on f or t he N S2 and
EW2 repeaters is augmented w ith a special programma-
ble connection allowing bidirectional communication be-
tween local-bus segm ents. Thi s option is primarily used to
implement l ong, tri-state buses .
D escrip tio n (Continued) The Cell Structure
Th e At mel cell (Fi gur e 4) is simple and small and yet can
be progra mmed to perform all t he logic and wiring func-
tions needed to i mplement any digi tal cir cuit. Its four sides
are functionally identical, so each cell is completely sym-
metrical.
Read/write access to the four local buses— NS1, EW1,
NS 2 and EW2— i s controlled, in part, by four bidirectional
pass gates connected directly to t he buses. To rea d a lo-
cal bus, the pass gate for that bus is turned on and the
thr ee-input multipl exer is set accor dingly. To write t o a lo-
cal bus, the pass gate for that bus and the pass gate for
the associated t ri-state dri ver are both t urned on. The two-
input multiplexer supplying the cont rol signal to the drivers
permits either: (1) active drive, or (2) dynamic tri-stating
controll ed by t he B i nput. Turning bet ween LNS1 and LEW1
or betw een LNS2 and LEW2 is accom plished by t urni ng on
the two associ ated pass gates. The operations of readi ng,
w riting and t ur ning are subject to the re striction t hat e ach
bus can be involved in no m or e than a sin gle operation.
In addition to the four local-bus connections, a cell re-
cei ves t wo input s and provides t wo outputs t o each of its
North (N), South (S), East (E) and West (W) neighbors.
These inputs and output s ar e divided into two classes: “A”
and “B.” There is an A input and a B input from each neigh-
boring cell and an A output and a B out put drivi ng all four
neighbors. Between cells, an A output is always con-
nected t o an A input and a B output to a B i nput.
Within the cell, the four A inputs and the four B inputs enter
two separate, independently configurable multiplexers.
C ell f lexibility is enhanced by allowi ng each multipl exer to
select also the logical constant “1.” The two multiplexer
outputs enter the two upstream AN D gates.
Dow nstream from these two A N D gates are an E xclusive-
OR ( XOR) gat e, a regi ster, an AN D gate, an inve rter a nd
tw o four-input multiplexers produci ng the A and B out put s.
These mul tiplexers are co ntrolled in tandem (unli ke the A
and B input multiplexers) and determine the function of the
cell.
•In S tate 0— cor respond ing to t he “0" inputs of the mul-
tiplexers— the output of the left-hand upstream AND
gat e is connected to the cel l’s A output , and the output
of the right-hand upstream AND gate is connected to
th e cell’s B out put.
•In S tate 1— cor respond ing to t he “1" inputs of the mul-
tiplexers— the output of the left-hand upstream AND
gate is connected to the cell’s B output, the output of the
right-hand upstream AND gate is connected to the cell’s
A outpu t.
•In S tate 2— cor respond ing to t he “2" inputs of the mul-
tiplexers— the XOR of the outputs from the two up-
stream AND gates is provided to the cell’s A output,
2-6 AT6000/LV Series