Randy Walsh Wrote:

>Need help with a little hardware RS232 inteface.
>
>Description: I've created a PC stepper motor interface using a 16c84 and a
>2003.  I'm currently doing Serial I/O straight from the 16c84 to the PC
>
>Question: If I use 1 of then 2003 drivers to boost the TX line (from pic to
>PC) to +12 volts, would this damage the PC?  (I thing that the RS232 spec
>is only +10 volts), what must I do to safely drop the voltage to 10 volts?

No.  RS-232 is up to 15 Volts.

Where you may have your problems is with the negative voltage generation.
Your PC (like mine) may "read" 0 Volts as a "Mark" and actually require a
negative voltage.

There's a simple circuit for using the RX Negative Voltage.  Please correct
me if I'm wrong:



             |
             |     10K Resistor
  PIC   RXIn |-----^^^^^^-------------------+-------------------- From PC
             |                              |
             |                              >
             |                              < "Pull Down" Resistor
             |                              >
             |                              |
             |                              +-------------------- To PC
             |                              |
             |           Resistor         |^
        TXOut|-----------^^^^^------------|
             |                            |\
             |                              |
             |                            To +5 - +12 Volts
             |

This will send a Negative Voltage nominally and then send a Positive voltage
when the TXOut Line is High.

Have I got the circuit correct?  I typically use a DS275 which does all this
for me.

myke

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