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Step7<br />
Wire· the SN7493 counter as shown in Fig. 6-19. You will nee<br />
use the input port and the output port from the previous steps<br />
this experiment. You will also need two NOR gates, as shown<br />
Fig. 6-19. A single SN7402 chip will provide these gates. Do<br />
+5<br />
SN7402<br />
49317 14<br />
12<br />
INP A A<br />
DO<br />
WR<br />
INP B B DI<br />
TO INPUT<br />
RO<br />
D2<br />
49319 PORT*<br />
11<br />
RO D<br />
D3<br />
10<br />
SN7493<br />
*GROUND INPUT BITS D7-D4<br />
Fig. 6-19. Test circuit schematic used to check SN7493 counter chips.<br />
substitute an SN74L93 counter for the SN7493. Remember to gro<br />
the unused inputs on the input port.<br />
Step 8<br />
Write a short test program that will exercise the reset functi<br />
on the counter, and one that will test the ability of the comput<br />
to clock the counter and increment its count by one.<br />
We used the following program:<br />
10 POKE 49318,0<br />
20 IF PEEK(49319) > 0 THEN 1000<br />
30 PRINT "RESET TEST OK"<br />
40 FOR C = 1 TO 15<br />
50 POKE 49317, 0<br />
60 IF PEEK(49319) C THEN 1010<br />
70 NEXT C<br />
80 PRINT "COUNT TEST OK": END<br />
'<br />
1000 PRINT "RESET FAILURE":END<br />
1010 PRINT "COUNT FAILURE AT "; C: END<br />
148
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