>I have a PIC device that connects to my PC via serial port
>for constant communication.
>
>I would like to have over 10 PIC devices connected to my PC
>somehow for communication.
>
>However, i would not like to buy some sort of expensive
>multi serial port card for it.
>
>What sorts of things can i do to over come this problem?
>Potentially i would like to use over 10 of these PIC devices at once.


I used to work on computer terminals that used a multi-drop RS232 levels in
a polled terminal environment. They did this by having a resistor that went
from the TX data line to -12V, and then pulled the line to +12V using a PNP
transistor. This transistor is used in place of the normal MAX232 type
device. You then also need a suitable RS232 receiver at each PIC, but with a
higher input impedance than normal.

You then need to work out a protocol where the software in the PC calls up
each device in turn, telling it when to transmit the data to the PC.

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