output always with weak pull down?

[ipq]

Hello,

My mcu is driving an optotriac with a pin set up as an output. The problem arises when the mcu is restarted, then the output is undetermined and it is activating the opto.

Is there any way to avoid the use of weak pull down resistors to avoid this?

The point is...Is there anyway to avoid that "output dance" when the mcu is restarted (I mean by code)?

Thx

[asmallri]

[Ttelmah]

Actually there may be.

Problem is that CCS by default sets the TRIS, before they output the value. This can give one cycle of the signal being driven high, when you want it to go low. This may well be the 'dance' being referred to.

In all honesty this is one place where using FAST_IO is definitely called for. The sequence then becomes:

Set the output register to the level you want.
Now set the TRIS.

Alternatively, if using standard_io, simply use getenv, to get the lat register for the port, and set this to the level you require, before calling the output instruction.

[temtronic]

Another possible way is to design using 'active low logic' and have a real pullup in parallel with the opto device input.
This would ensure the opto is always off until a solid low or '0' is sent to it.

Jay

[ipq]

hello everybody,

Ttelmah: We have been trying to use fast_io, but with no success.

temtronic: You mean an AND gate?

Thx

[drolleman]

no what he means is put the resistor to 5v to opto then to mcu so when you want it activate it you send a output low.

[Ttelmah]

and what is your problem with fast_io?.

What port are you on?.
What peripherals are you using on the port?.
What pins are you using?.
What TRIS setting are you using?.
etc..

[wangine]

Put brownout reset on your fuse, anode of opto on PIN_x0 and cathode on PIN_X1, should avoid that "output dance", any random state on port, high or low can't trigger the opto.