Re: PIC USART troubles

hybrid_snyper wrote:
Hello all,

Im in a bit of a desperate situation. I am trying to get my PIC 16f876
to talk to a Ericsson T28. The T28 has both TX/RX pins and I have
connected them directly to the TX/RX pins on my PIC. I measured the
voltage across the VDD and GND on the phone and I am running my PIC at
the same voltage. I have written a simple program that should send the
AT command AT+CFUN=0 this should turn the phone off. However this is
not the case, I am not sure if i am understanding the USART spec,
people have mentioned something about inversion but i thought this
would only apply when wishing to reach RS232 levels.

Unfortunately, the internal USART outputs the signal using reversed polarity
so that a level converter (like a MAX232) will work with it. If your T28
outputs a signal that an ordinary PC serial port can read, then you will
need to invert the output of the PIC so that it can talk to the T28. When
the phone is sitting idle, what is the voltage on the TX and RX pins?
Compare those with the PIC.


I have connected the phone to my PC and ran hyper-terminal with the
spec baud 9600, 8bits, 1 stop bit and no parity, i believe that i have
set the PIC up correctly however the phone just isnt responding.

That answers that. You need to invert the output of the PIC. Use an
inverter, logic gate (NAND, XOR, or NOT) or whatever you wish to flip it
over. Or you could bit-bang it. AFAIK, the PIC has no ability to invert
the output of the USART, stupid as that sounds.

Could any one give any tips, also it may be worth looking at an older
post of mine that will over a bit of background at what I have been up
to.

http://groups.google.co.uk/group/sci.electronics.basics/browse_thread/thread/b7de71f84dcb6d5b/560a336845019a11?lnk=gst&q=hybrid_snyper&rnum=2&hl=en#560a336845019a11

Kind regards

Wayne


.