On Mon, Apr 14, 2003 at 11:57:56AM -0400, Byron A Jeff wrote:
> On Mon, Apr 14, 2003 at 11:27:16AM +0200, Werner Soekoe wrote:
> > Quick Question:
> >
> > If I use the USART of the PIC16F627 (or any other PIC with an USART) in
> > async mode to communicate with a PC via a RS232 serial port, do I need to a
> > transceiver chip such as the MAX232, or will it work without the
> > transceiver?
>

Forgot something. Oops.

> [... ]
> The input needs voltage limiting. I use a current limiting resistor and a
> zener diode. The diode limits voltage in both directions: positively at its
> rated voltage (I usually use a 4.7V one for this application) and -0.6V in
> the negative direction.

Here's what I forgot.

For the input, you still need an inverter for the hardware USART. Simply run
the connection between the resistor and the cathode of the zener into the
inverter input. Then take the inverter output and tie it to the PIC USART
input pin.

And to reiterate...

The MAX232 style chips are the simplest way to accomplish the task because
they incorporate both the level conversion and voltage inversion. But there
are other options with possibly more handy parts.

BAJ

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