TAMS / Java / Hades / **applets** (print version): contents | previous | next#### GAL demonstration: complex functions

**Description**

This circuit demonstrates two more examples of logical functions
using the **GAL** or **generic array logic** structure.
For a description of the circuit structure see the previous two applets.

In this demonstration, the output enable of the output cell blocks
is set to low, enabling the tristate driver.
Also, the XOR bit of each output cell is selected, so that the
direct (non-inverted) output of the OR-gates is passed through to the
Y_out output.
Additional external inputs C and D have been added (on the right of
the schematics), feeding back into the AND fuse matrix.

The programming in the upper GAL block implements the
logical function (AB + AC + BC), resulting of the ORing together
of the three terms (AB), (AC), and (BC) from the first, second, and
third rows of the fuse matrix.
(Keeping both the A and /A fuses intact in the fourth row results
in a constant zero value for that row).

The programming of the lower GAL block implments the XOR function
of inputs A and B.

+ = fuse ok
. = fuse blown
A /A B /B C /C D /D function
+ . + . . . . . A AND B
+ . . . + . . . A AND C
. . + . + . . . B AND C
+ + . . . . . . zero
total:
AB or AC or AD
+ . . + . . . . A AND /B
. + + . . . . . /A AND B
. . . . . . + + 0
. . . . . . + + 0
total: A xor B

Run the applet | Run the editor (via Webstart)

Impressum | 24.11.06

http://tams.informatik.uni-hamburg.de/applets/hades/webdemos/42-programmable/20-gal/GAL-demo2_print.html