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From: lynch@cci.de
Subject: Win NT + Object Ada: serial port I/O
Date: 1999/02/03
Message-ID: <79952r$2t$1@nnrp1.dejanews.com>#1/1
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Date: 1999-02-03T00:00:00+00:00
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Hi,

I have been asked to write a DLL which will be used to talk to a display (LCD)
connected via an RS-485 serial line (DIN 66 019 protocol). The card apparently
comes with a driver which makes it act like a standard COM-Port.

Rather than fork out the $XXX for something like Visual C++ (and a new HDD) I
would like to develop using the Object Ada we already have.

Does anyone have any information/experience programming serial ports in Ada on
a Windows platform? I can think of two ways to do this:

1) Use the standard Ada.*.IO routines on the file "COM1:". I tested this with
   a VT420 on the other end and came across two problems:

   a) It seems the port needs to be "initialized" by calling MODE COM1: in a
      console window, even though the settings are exactly the same as those
      in the windows control panel.

   b) I need a timeout capability for the reply from the LCD/Terminal.
      Using Get or Get_Immediate without "Available" blocks indefinitely,
      all attempts to use Get_Immediate with loops and timers have failed.
      (Available seems to be _always_ false!?)

2) Use the Win32Ada binding with CreateFile, SetCommTimeouts etc. however the
 help file provided with Object Ada is utterly useless. I have yet to find 
the section which "describes [...] the transformation rules (from C to Ada)" 
Also the guy who will be using this DLL is worried about all the type 
conversions etc. ("why use an Ada compiler if you're writing C anyway...")

Are there any alternative (higher-level) "COM-Port"-Bindings available?
All I need to do is write a stream of ASCII characters and read characters
with a timeout after x ms, in case somebody pulled the plug or whatever.

If anyone has some sample code that accesses a COM-port using Object Ada
I would be most grateful for a quick peek at it! (This is my second-ever
MS-Windows project, I hope it will be my last...)

Cheers,
Andrew.


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