I'm trying to perform communication with a Motorola MPC5606B microcontroller using a cable that I already had previously. Using this cable will make things easier in my lab because everyone has one the same. But I have a concern: there is a diode 1N4007 in line with Vcc.
simulate this circuit – Schematic created using CircuitLab
So, because of the diode on the VCC line, the I/O voltage can be greater than that specified on the datasheet. The datasheet specification is given in the figure below.
So, my concern is: if the voltage on the I/O pin is 0.3V greater than Vcc, but below 6V, can it damage the I/O pin of the microcontroller?
Best Answer
The simple answer is yes, it can. The specifications clearly show what the absolute rating is, and you are violating it, since there may be cases where VDD is 4.3V but your input is 5V. This means that the manufacturer is not guaranteeing that the part will function correctly.
The real question is, will it probably work? The answer is maybe. If there's not much current going into the pin (i.e. whatever you're connecting to the input has a high output impedance), it's probably fine. All your IO pins will have internal diodes connected to VDD and GND. These are what will clamp the input voltages, and these are what will break if you put too much current through them. They are usually rated for very small amounts of current. It looks like, in your case, they may be rated for 10ma, so if you're putting 1ma through them, that might be alright.