com (serial port) library behvior

[edward kaeufer]

I am trying to use pb in a rs485 environment and have 2 questions.

1. Opened com port with option "rs" specified.
Does this disable the functionality?
aka: rts does not change states (on, off) before,
during and after transmission of data?

2. Is "print #n" blocking?
aka: program control returns after data completely sent?

Thanks
Ed



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[Mel Bishop]

1. Yes. If you have RS specified, its state is immaterial. RS
will always be ignored. Ditto with CS, DS and CD.

2. Control will probably be returned after writing the info
to the comm buffer. Not necessairly to the port itself.

Word of note: The com port(s) on a computer are RS-232. I don't
know if they are compatable with RS-485 devices. If you have
this configuration, you may need a converter for successful
communication.


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[edward kaeufer]

The RS option deals with "request to send", an outboard signal
which is changing states apparently by the pb com driver.
My RS485 device uses the RTS to control data flow...

Originally posted by Mel Bishop:
1. Yes. If you have RS specified, its state is immaterial. RS
will always be ignored. Ditto with CS, DS and CD.

2. Control will probably be returned after writing the info
to the comm buffer. Not necessairly to the port itself.

Word of note: The com port(s) on a computer are RS-232. I don't
know if they are compatable with RS-485 devices. If you have
this configuration, you may need a converter for successful
communication.

------------------

[Mel Bishop]

Originally posted by edward kaeufer:
My RS485 device uses the RTS to control data flow...

Then you need to NOT put the RS in the "open com:x" parameters.
If you do specify the RS, CS, DS or CD in the "open" statement,
these control signals will be ignored regardless of the com
port pin state.

Assuming your external device defaults to hardware flow control,
just open the com port with the basic parameters:

"Open "Com1:9600,n,8,1""

should do the trick. Make sure your device is on before you
bring up the program. Otherwise, you will probably get a device
time-out error.


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[This message has been edited by Mel Bishop (edited June 11, 2003).]