ATTINY85 digital pins grounded when conencted to power !

Hi friends. I have a problem with attiny85. the problem is when I power up the attiny85 the digital pins grounded with GND also when I using multi meter buzzer test, the buzzer activated between the GND and digital pins. any way to fix ? thanks.

can anyone help ?

You can't use a continuity test like that when the device is powered up. Instead, test the voltage on the pins.

There are three possibilities:

  1. You previously uploaded a sketch which sets all pins as output, and wrote them either LOW or did not subsequently call digitalWrite() on them. The DMM will likely mistake this for a low resistance, and behave accordingly - at least if the negative/black wire is connected to ground - but as noted above, measuring resistance is not meaningful. In this case, upload Bare Minimum using your ISP programmer and you should be all set.

  2. The t85 is connected wrong.
    2a. You have not actually connected Vcc, so the pins are connected to ground through the protection diodes to Vcc, and your DMM sucks. A good DMM will not show continuity here, but rather an erroneous resistance reading (because a diode does not have a defined resistance, the number you would get trying to measure it can only be wrong), but I would not be surprised if cheap DMMs would.
    2b. The pins are actually shorted to ground due to a soldering or wiring error, or board is resting on a conductive surface connected to ground, or something of the sort.
    In either case, correcting the wiring should resolve the situation, unless the improper connections have damaged the part.

  3. The chip has been horribly abused, and all the pins have failed shorted to ground, which is a common failure mode when chips are damaged, particularly by abuse like connecting power backwards, or applying voltages higher than Vcc or lower than Gnd to I/O pins. The t85 in this case is ruined and should be replaced.

BJHenry:
You can't use a continuity test like that when the device is powered up. Instead, test the voltage on the pins.

thanks for reply. the voltage between the GND and digital pin3 is 0 and the ohm is 26.9 ohm. when I connect external interrupt to pin 3 the circuit is grounded.

DrAzzy:
There are three possibilities:

  1. You previously uploaded a sketch which sets all pins as output, and wrote them either LOW or did not subsequently call digitalWrite() on them. The DMM will likely mistake this for a low resistance, and behave accordingly - at least if the negative/black wire is connected to ground - but as noted above, measuring resistance is not meaningful. In this case, upload Bare Minimum using your ISP programmer and you should be all set.

  2. The t85 is connected wrong.
    2a. You have not actually connected Vcc, so the pins are connected to ground through the protection diodes to Vcc, and your DMM sucks. A good DMM will not show continuity here, but rather an erroneous resistance reading (because a diode does not have a defined resistance, the number you would get trying to measure it can only be wrong), but I would not be surprised if cheap DMMs would.
    2b. The pins are actually shorted to ground due to a soldering or wiring error, or board is resting on a conductive surface connected to ground, or something of the sort.
    In either case, correcting the wiring should resolve the situation, unless the improper connections have damaged the part.

  3. The chip has been horribly abused, and all the pins have failed shorted to ground, which is a common failure mode when chips are damaged, particularly by abuse like connecting power backwards, or applying voltages higher than Vcc or lower than Gnd to I/O pins. The t85 in this case is ruined and should be replaced.

thanks for reply. now the problem solved by protecting the circuit with 1N4148 Diode on GND side