how to steal power from PIC instead of PC RS-232 port

[Oliver Lai]

I have a board, which outputs data with RS232 (MAX3227), the board get power out of PC RS232 port ( or from TD/RTS/DTR).

Now I want to work this board with PIC micro controller, need to supply power to the board. Can somebody tell me how to supply it? If it is supplied by MAX232 (possible?), which PIN are used to replace TD/RTS/DTR?

Thanks,
Oliver

[SherpaDoug]

I suggest you hook up the board to a PC and measure the voltages on each pin. Then connect the board to your PIC and try to simulate each of the voltages you measured, excluding those supplied by the PIC.
Another probably more difficult method would be to measure the current on each pin of the connection to the PC. The pin with the highest current is probably the power supply or ground.
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[Oliver Lai]

I have tried in the following links:

keep the data link unchanged, add power from external power supply:

D9 PIN4 and PIN7 connect to +10V,
PIN5 is ground.

Still no data was captured (':evil')

[languer]

You may have already done this, but have you monitored the suspect (power) signals Not with a DMM but with an oscilloscope?

The reason for the question is that I see you've already tried supplying power to the RS232 device (black box) with no luck. So I wonder if the device is not powered from this signals, but actually uses them for handshaking? What is the port setting of your COM2 port (where you originally got your device working)?

One other thing you could try is to connect this three (or two) lines from the PC's COM2 and the actual TX/RX lines to the PIC. Does it work now? It should if it is powered by them. It should not if it is expecting some sort of handshaking?

Hope it helps.

After writing this, I decided to check on this MAX3227 device. Nice little thing, do you know it has an "AutoShutdown Plus" feature? When you disconect the cable from the device (i.e. when the device does not sense activity) or when there is no activity for 30secs, it will automatically shut down (no output signals at all; does this ring a bell ). Anyway I thought you may want to check on this (if you have not done so already), but I think that it is expecting some sort of handshake from your PIC. The datasheet mentions a way of overriding this feature, so you may also want to look at that.