pic16f88 & voltage

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- 14th February 2009, 02:30
rdxbam

pic16f88 & voltage

i have a pic16f88 & xbee on the same breadboard. the pic should run at in input V between 2.0v to 5.5v.

on the breadboard i have a 7805 for the 5v to the pic and a LD3.3 regulator for the xbee.

however, having two voltage regulators is causing a problem when the xbee gnd is on the same rail as the 5v. that issue is probably evident to an EE, which I am not.

Yet, I can't get the pic16f88 to function with 3.3v. At this point I was hoping to have only one voltage regulator and be able to power the pic & xbee.

is there a programmatic setting i'm not using or should be using to get this pic to run with 3.3v ?
- 14th February 2009, 10:30
mackrackit

What OSC are you running the PIC at?

Look at the electrical specifications in the PICs data sheet to see what speeds work with different voltages.
- 14th February 2009, 13:18
Acetronics2

Hi,

Which inputs do you use for Xbee ???

Alain
- 14th February 2009, 13:19
peterdeco1

It looks like the 16F88 needs a minimum of 4V to operate. The 16LF88 needs only 2V. Try the LF part, use 3.3V for both and turn off Brownout Detect.
- 15th February 2009, 00:38
rdxbam

mackrackit

for this project, i have "DEFINE OSC 8"

>>Look at the electrical specifications in the PICs data sheet to see what speeds work with different voltages.

i've missed something there, thx for the reminder

*************************************
Acetronics

>Which inputs do you use for Xbee ???

pin 1 for 3.3Vcc
pin 3 for input from RB5(tx) from pic

Alain

*************************************
peterdeco1,

>It looks like the 16F88 needs a minimum of 4V to operate. The 16LF88 needs only 2V. Try the LF part, use 3.3V for both and turn off Brownout Detect.

actually i didn't see that in the datasheet i have but i'll look again. in the meantime i'll pick up some 16LF88's which are better suited to this particular prototype session.

thx
- 15th February 2009, 10:38
Acetronics2

Bad way of asking the Question ... ( I think )

Quote:

>Which inputs do you use for Xbee ???

pin 1 for 3.3Vcc
pin 3 for input from RB5(tx) from pic

Hi,

I think I didn't write it correctly ...

Which inputs of the PIC do you use for Xbee reading ...

Alain
- 16th February 2009, 04:53
rdxbam

Quote:

Originally Posted by Acetronics

Hi,

I think I didn't write it correctly ...

Which inputs of the PIC do you use for Xbee reading ...

Alain

no problem, i read backwards randomly at times, so maybe i mis-read the question.

i use pin RB2(rx) is the only reading from the xbee currently.
- 16th February 2009, 06:06
rdxbam

Quote:

Originally Posted by peterdeco1

It looks like the 16F88 needs a minimum of 4V to operate. The 16LF88 needs only 2V. Try the LF part, use 3.3V for both and turn off Brownout Detect.

via the data sheet for the PIC16LF88-I/P on mouser's site i do now, see the pic16f88 listed at 4V.

thanks
- 16th February 2009, 08:48
Acetronics2

Quote:

Originally Posted by rdxbam

no problem, i read backwards randomly at times, so maybe i mis-read the question.

i use pin RB2(rx) is the only reading from the xbee currently.

Hi,

RB2 is then a Schmitt trigger Input ... if used for RX ...

Can a 5v Powered schmitt Trigger input read 3v3 levels ??? ...

Good Question !!!

Alain
- 17th February 2009, 09:09
rdxbam

Quote:

Originally Posted by Acetronics

Hi,

RB2 is then a Schmitt trigger Input ... if used for RX ...

Can a 5v Powered schmitt Trigger input read 3v3 levels ??? ...

Good Question !!!

Alain

indeed, great question and prompts me to research more:

via p#11 of the datasheet from http://ww1.microchip.com/downloads/e...doc/30487c.pdf ...

i'm using pin RB2 as [I]nput and not using the buffer as a Schmitt trigger input. Pin RB2 as [I]nput is for ausart.

the Schmitt trigger input would be for serial programming ICD or low voltage ICSP programming but not on pin RB2, unless for SPI data out, which in my case it is not.

is that how you read it?

thx
- 17th February 2009, 09:14
rdxbam

Quote:

Originally Posted by Acetronics

Hi,

Can a 5v Powered schmitt Trigger input read 3v3 levels ??? ...

[...]

Alain

on another board with a pic16f88 with RB2 reading from pin2 on the xbee sitting on a xbib-r-dev board, the data is read just fine. yes, RB2 can read 3.3v levels.