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program. You may forgotten steps to dear the APand<br />
DANGER displays from your screen. You may also<br />
forgotten to use three POKE commands to load the informarequired<br />
by the USR command. You can do this without addanother<br />
step to your program, simply type in the POKE commands,<br />
followed by a RETURN. They only need to be executed<br />
The commands for printing spaces at lines 700 and 800 are used<br />
clear the APPLIANCES and DANGER signals that are displayed.<br />
program could be much more complex, containing steps to use<br />
""'"n',_, video, or to fl.ash the display when an emergency condition<br />
sensed by the program. You should realize by now that the softcan<br />
handle both mathematical and logical operations. You<br />
also see that the use of assembly-language subroutines is not<br />
difficult<br />
You may tum off the computer, although the assembly-language<br />
operation program will be used again. The input port will also<br />
used again, so do not dismantle your circuit.<br />
EXPERIMENT NO. 8<br />
CONSTIU.!ICTiNG AN OUTPUT PORT<br />
The purpose of this experiment is to have you construct a simple<br />
output port and investigate its use.<br />
In this experiment, a simple 8-bit latch circuit will be used to<br />
construct an output port. The output port will be used in this experiment,<br />
and in some of the following experiments, in which it<br />
will be necessary to transfer information to external devices. Two<br />
quad latch integrated circuits will be used.<br />
FUNCTION TABLE<br />
(Each Latch)<br />
INPUTS<br />
OUTPUTS<br />
0 G a Q<br />
L H L H<br />
H H H L<br />
x L Oo 50<br />
H =high level, L = low level, X =irrelevant<br />
0o =the level of 0 before the high-tolow transition of G<br />
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