II.2.6 How to Test Programmed GALs

Once the GAL has been programmed, the question remains, "does it work the
way you envisaged it?". Answering this question is the purpose of the
GAL-Checker.

In order to verify the GAL's functions, you must of course first plug
the GAL into the programmer's socket, and select the correct GAL-type.
Now you can select the menu item GAL-Checker.

In the middle of the screen you'll see a symbolic GAL displayed. In this
GAL, you'll see a number of 'I's and 'O's. The 'I' stands for Input and
the 'O' for Output.
The 'O' is a gadget. By clicking on the 'O' it turns into an 'I' and
clicking on it again it becomes an 'O' again. In other words, you can
determine if this pin is to be used as an input or an output.

If a pin is an input, then you can select from another gadget if the pin
is to be in a  "High" ('H') or in a "Low" ('L') state. An output can
assume three states: 'H' (High), 'L' (Low) and 'Z' (high impedance).
The current state is displayed near the corresponding pin.

If you're using the GAL from the above example, pin 19
must be defined as an input (="A") by clicking on the 'O' (the one at pin 19),
since this pin was defined as an input during  programming in the above
example.

The inputs of the AND gate are:  pin 19  (="A"),  pin  1 (="B"), pin 2 (="C").
The output is pin 18 (="W").

If you now  set the inputs of the AND gate HIGH (by clicking on the gadgets),
the output (=pin 18) should also go HIGH.  If it doesn't work or if the output
also goes high with other combinations of input levels, then the fault is
probably in the source file.  The error should be corrected in the source file.
The GAL must then be erased and reprogrammed (a GAL can be erased and
reprogrammed at least a hundred times). In this manner the whole GAL can
be fully tested, and if no errors are detected, it can be used in your circuit.