current sourced/sinked when connecting two BS2's

RichardF

If I connect a pin of one BS2 ,·set to·output HIGH,·to a pin on a·second BS2 set to input, what will be the current sourced/sinked (common ground, of course)? This is assuming there are no resistors installed on the pins (not a·Homework Board).
Thanks,
Richard·

marzec309

Not sure exactly on how much current will be sinked into the second BS2, but with the pin set as an input is not much at all probably in the uA (0.000001 Amp in 1uA)range. But I would recommend a resistor between the two Pins. If One BS2 was driving its pins high and the other pulled its pin low, you would have a direct short and damage One or both BS2's. The resistor would limit the current between the two. Its a good safty margin and resistors are cheap.

allanlane5

I believe the input impedence on the BS2 is around 10 megohms, so it takes VERY little current for the BS2 to read the input signal as "high" or "low".

The problem is as was stated above -- if the 'input' BS2 accidentally sets that pin to an 'output', and 'outputs' a LOW, you'll have a dead-short (very low resistance connection) between Vdd and Vss, which will burn out the transistors behind one or both pins. A 220 ohm resistor between the two I/O pins will prevent damage should that happen.