I would like to know if a 74HC245 can drive the input pins of an ATmega16.
The bus transceiver opens the data flow toward the ATmega16, which has the port set as input.
So far, the ATmega16 drives the 74HC245 with no problem, however, I still have some problem in always reading the correct value from the 74HC245.

After replacing the 74HC245 with a 74LS245, the problem seems resolved, but I can't understand the root problem with the 74HC245. Which things should I care about?

  • \$\begingroup\$ Never leave CMOS inputs floating. Make transitions swift. Use a supply voltage such that voltages are acceptable for both sides, have a bypass capacitor (or two) close to each package. If you want other to help analyse a problem, supply information (in your question), starting with supply voltages (ATmega16, 74HC245, 74LS245). Spell out some problem, graphs welcome. \$\endgroup\$
    – greybeard
    Mar 24 at 21:28
  • \$\begingroup\$ What is the correct value if the bus is disconnected? \$\endgroup\$
    – user253751
    Mar 24 at 21:33
  • \$\begingroup\$ Sometimes the output from 74hc245 seems to oscillate. After the 74HC245 is enabled, the output is stable, but after a while it starts to oscillate. I'll begin following the suggestion from greybeard and tomorrow will check the powersupply adding some extra bypass capacitor. When the bus is disconnected the wires between the ATmega16 and the 74HC245 seems to follow what is happening on the other side of the 74HC245. These wires are between two devices in high Z. Mumble defective transceiver? \$\endgroup\$
    – ozw1z5rd
    Mar 24 at 21:57
  • \$\begingroup\$ (oscillate smells of illegal potential at inputs: can you inspect/include an oscillogram? (of both input&output, preferably.) (Note the nodes common to transceiver&MCU deserve pullups or pulldowns - can those be configured when specifying MCU pins as input?) \$\endgroup\$
    – greybeard
    Mar 24 at 22:24
  • \$\begingroup\$ I noticed that also the 74LS245 is suffering from the same issue, it could be a bad contact problem. Removing and inserting the new chip stressed the breadboard mechanically. For completeness, I'll update the question asap with more info. \$\endgroup\$
    – ozw1z5rd
    Mar 25 at 10:49


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