laser
Junior Member level 3
pic latch up
Hi all.
I´m working on a project wich uses a PIC 16F877 to comunicate asynchronously on a long line of several hundred meters, between a master unit and several slave units.
The way used for communication is very similar to RS485, on wich a 3 wire system is used (two positive differential wires plus GND), to transfer data in a differential way.
The only diference in my case, is that my slave units use this same line as the power source, and the way they respond is by shorting the positive lines also in a differential way.
Now, the ideia is ok, and it works fine, but I have one little problem:
Everytime I plug a new slave unit to the line, on the already connected slave units, the pic inverts it´s I/O outputs for a period of time of 72mS or more, causing undesired results.
I´ve also notisted a similar behavior everytime I touch the OSC CLKIN pin with a screw driver.
Power Up Timer and Brown-out Detect are both on, and a reset would be welcome in a supply voltage drop situation, but not the inversion of the values on the I/O pins.
I read somewhere that this behavior is called Latchup, but what is the cause of this, and what can I do to avoid it?
I´ll apretiate any ideias.
Thanks.
Hi all.
I´m working on a project wich uses a PIC 16F877 to comunicate asynchronously on a long line of several hundred meters, between a master unit and several slave units.
The way used for communication is very similar to RS485, on wich a 3 wire system is used (two positive differential wires plus GND), to transfer data in a differential way.
The only diference in my case, is that my slave units use this same line as the power source, and the way they respond is by shorting the positive lines also in a differential way.
Now, the ideia is ok, and it works fine, but I have one little problem:
Everytime I plug a new slave unit to the line, on the already connected slave units, the pic inverts it´s I/O outputs for a period of time of 72mS or more, causing undesired results.
I´ve also notisted a similar behavior everytime I touch the OSC CLKIN pin with a screw driver.
Power Up Timer and Brown-out Detect are both on, and a reset would be welcome in a supply voltage drop situation, but not the inversion of the values on the I/O pins.
I read somewhere that this behavior is called Latchup, but what is the cause of this, and what can I do to avoid it?
I´ll apretiate any ideias.
Thanks.