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We have been making a Register. When we write all ones, it works fine. When we enable it back onto the bus using 74LS245, it doesn't enable. We used our Multimeter to measure the volts. It seems to have 1 Volt when the Output Enable is high, and then 0 Volts when Low. This is number one not enough to power our LEDs, and number two not the output we expected.

Note; this is based off of Ben Eater's model.

enter image description here

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  • \$\begingroup\$ Okay here \$\endgroup\$
    – Katido 622
    Apr 19 '20 at 4:05
  • \$\begingroup\$ Okay thanks for that. \$\endgroup\$
    – Katido 622
    Apr 19 '20 at 4:24
  • \$\begingroup\$ no, not a link to the image, but the image itself ... corrected it for you ... should be visible once it is accepted \$\endgroup\$
    – jsotola
    Apr 19 '20 at 4:28
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When you see an "inbetween" voltage on a digital bus (i.e. not logic "0" and not logic "1"), the cause 99.7% of the time will be bus contention. i.e. you've got two outputs connected together, one is pushing a "high", the other a "low". And you end up somewhere inbetween.

Besides double-checking ALL your wiring, suggest you check the "DIR" signal, make sure that's really logic HIGH. If it's logic low, then you'll be driving the LED's with the '245' and the '173's at the same time.

Did you build this on a plugboard? They're notoriously finicky. Wiggle wires.

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  • \$\begingroup\$ I'll try to do this. My DIR signal seems to be 5.2 Volts, and, this was made on a breadboard. \$\endgroup\$
    – Katido 622
    Apr 19 '20 at 16:16
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I suspect that you have forgotten to connect the Vcc and GND pins to the power supply. These connections are not explicitly shown on the schematic, but they are always required.

If you don't connect power and ground, then the chip can actually be powered by a logic 1 on an input pin. It's not a very good power supply, but it can cause you to see non-zero voltages on output pins. If you set all of the inputs to 0 and that causes all of the output pins to go low, this is a sign that you might have forgotten the power connections.

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  • \$\begingroup\$ I will try to do this (at least without shorting my circuit like I've done twice). \$\endgroup\$
    – Katido 622
    Apr 19 '20 at 16:16

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