Re: PIC USART troubles

On Mar 3, 7:31 pm, "Anthony Fremont" <spam-...@xxxxxxxxxxx> wrote:

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.

A PC can only read the signal when i use a special data cable,
dissected the cable and found a max232 in it, therefore any signal
conversion was done in the cable. I was under the impression that i
would not need a max232 to connect the PIC and T28 directly because
the MAX232 is used to bring a signal to RS232 standards.


When the phone is sitting idle, what is the voltage on the TX and RX pins?
Compare those with the PIC.

Voltage on TX is 2.7V

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.

Could i ask why this is, is the output from the TX meant to be neg?

Or you could bit-bang it. AFAIK, the PIC has no ability to invert
the output of the USART, stupid as that sounds.

Not sure what bit banging is but will look into it.


Thanks for the speedy reply.

Wayne



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