3.3 v logic or 5 v logic

guest453 · Guest

Hi all, i have the following code;

ccesaretto · Joined: 03 Mar 2009 Posts: 5

I had similar issues with the serial port. I resolved using an external oscillator rather than the internal one.

Guest · Posted: Tue Apr 07, 2009 4:42 am

Please have a look into the datasheet if the internal oscillator meets the requirements of max. 2% speed deviation at the serial port or not. Some combinations of clock and desired baudrate will not match. To figure out if you have a sampling/baudrate problem or not try other baudrates.

guest453 · Guest

Thanks guys,
Now it works.

bsturm · Joined: 23 Feb 2009 Posts: 29

What did you change? Did you have to add an oscillator?

guest453 · Guest

i disabled internal oscillator and enabled external and put an external oscillator.It worked.

bsturm · Joined: 23 Feb 2009 Posts: 29

I suspected that is what you had to do. I have had the same problem and I haven't fixed it yet. The internal oscillator seems to hold time very well, well within 1% when I measured it. But I still couldn't communicate with Hyperterminal or a serial LCD. I could communicate with my PicKit2 in serial mode no problem.

I captured my bits on a scope and the timing looked excellent, but still not working with Hyperterminal. I don't understand why it wouldn't work. I even adjusted my clock speed up and down a little, but still nothing. I don't need async comms at the moment, so I gave up. I am using my osc pins as IO, so adding a resonator would be difficult. I'm glad that you got yours working.

guest453 · Guest

well i used the code that i posted.i set the baudrate 9600 and i used 4 mhz crystal.i read pcd manual and i changed the first line of fuses statement like this

#fuses HS, PR, NOWDT then
#use delay(clock=4000000) for clock.I think when i tried higher baudrate it didn't work but i am not sure.I must check it tomorrow.Do you see nothing in the hyperterminal?

i set hyperterminal like this:

baud:9600
parity:N
stop bits:1
hardware:N

did you set hyperterminal like that.by the way mine worked i didn't spend time for the internal oscillator anymore:)

I wonder if anyone has a sample code for pic24fj128ga106 using four hardware uarts.If anyone shares i will apreciate.

bsturm · Joined: 23 Feb 2009 Posts: 29

I was getting garbage characters on Hyperterminal, smiley faces and what not. Sometimes it would work properly for a short time. I did have it set to 9600-8-N-1. I also tried 2400, 1200,300 and even 110 baud with no luck.

guest453 · Guest

Be sure about voltage levels. All must set to 3.3. Then be sure that your line transceiver is working(max232 ext.) Then use a simple code (echo a character) that works. If it doesn't work post your circuit and code:)

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

If it works sometimes and not others it sounds like the clock or the voltage is marginal. Try forcing a software UART and setting the baud rate 2% high or 2% low.
Run a test and show us what you expect and the hex or binary you get, not just "smiley face".
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bsturm · Joined: 23 Feb 2009 Posts: 29

Thanks for the suggestions. For now, I have moved on to other issues, and I am not actively working it. Serial communication was just a convenience item, not necessary at this time. I was just curious what the original poster had found. I will start by checking voltage levels when I get back to it.