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Serial i/o using Borland C++ Builder

Posted on 1997-06-22
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Last Modified: 2008-03-17
I'm trying to write a simple serial instrument controller using Builder.

There doesn't appear to be a specific object for the serial port. I need to select a port, set the parameters (speed, parity, etc.) and then read & write control records. I'll need to log and act on the read data continuously while the user accesses other menus too. Surely a common enough requirement? But since I'm new to Windows and Builder programming, I'd appreciate a fairly detailed answer...

Many thanks in advance.

John
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Question by:langlois
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3 Comments
 
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Accepted Solution

by:
md041797 earned 100 total points
ID: 1164035
Use the CreateFile API to get r/w access to your port:

HANDLE port = CreateFile ("\\\\.\\COM1", GENERIC_READ |
  GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL);

Then use ReadFile / WriteFile to r/w.  The system buffers the io so you don't have to worry about multi-threading.

Use BuildCommDCB() to set the port (similar to MODE command).

Use SetupComm() to make the port sane.

If you need more help, just tell me where you are having problems.


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Author Comment

by:langlois
ID: 1164036
Okay MD,

I've at least established communication which is encouraging. But I'm not exactly able to set up my instrument controller yet. When I do a ReadFile(), I get to hang and wait until the requested number of chars have arrived. Makes it kinda hard to handle variable length records which may not even arrive! So how do I read data _if_ it's there but return regardless? For the record, here's the relevant snip from my kludgy test code as it stands:

DCB            dcb;
HANDLE      hCom;
DWORD      dwNumberOfBytesWritten, dwNumberOfBytesRead;
BOOL      fSuccess;
char      buffer[1024];

//////////
hCom = CreateFile("\\\\.\\COM2",
    GENERIC_READ | GENERIC_WRITE,
    0,                                  // comm devices must be opened w/exclusive-access
    NULL,                               // no security attrs
    OPEN_EXISTING,                  // comm devices must use OPEN_EXISTING
    FILE_ATTRIBUTE_NORMAL,      // not overlapped I/O
    NULL                                // hTemplate must be NULL for comm devices
    );

if (hCom == INVALID_HANDLE_VALUE)
      Label1->Caption = "CreateFile(): Failed";
else
      Label1->Caption = "CreateFile(): Passed";

///////////
fSuccess = SetupComm(
    hCom,      // handle of communications device
    1024,      // size of input buffer
    1024      // size of output buffer
   );      

if (!fSuccess)
      Label2->Caption = "SetupComm(): Failed";
else
      Label2->Caption = "SetupComm(): Passed";

///////////
fSuccess = GetCommState(hCom, &dcb);

if (!fSuccess)
      Label3->Caption = "GetCommState(): Failed";
else
      Label3->Caption = "GetCommState(): Passed";

//////////
fSuccess = BuildCommDCB(
    "baud=9600 parity=N data=8 stop=1",      // pointer to device-control string
    &dcb                                                // pointer to device-control block
   );      
 
if (!fSuccess)
      Label4->Caption = "BuildCommDCB(): Failed";
else
      Label4->Caption = "BuildCommDCB(): Passed";

///////////
fSuccess = SetCommState(hCom, &dcb);

if (!fSuccess)
      Label5->Caption = "SetCommState(): Failed";
else
      Label5->Caption = "SetCommState(): Passed";

//////////
fSuccess = WriteFile(
    hCom,                                    // handle to file to write to
    "echo fred\r",                        // pointer to data to write to file
    10,                                          // number of bytes to write
    &dwNumberOfBytesWritten,      // pointer to number of bytes written
    NULL                                     // pointer to structure needed for overlapped I/O
   );      

if (!fSuccess)
      Label6->Caption = "WriteFile(): Failed";
else
      Label6->Caption = "WriteFile(): Passed";

//////////
fSuccess = ReadFile(
    hCom,                              // handle of file to read
    buffer,                              // address of buffer that receives data
    16,                                    // number of bytes to read
    &dwNumberOfBytesRead,      // address of number of bytes read
    NULL                               // address of structure for data
   );      

if (!fSuccess)
      Label7->Caption = "ReadFile(): Failed";
else
      Label7->Caption = "ReadFile(): Passed";

buffer[dwNumberOfBytesRead]='\0';
Label8->Caption = buffer;

/////////
CloseHandle(hCom);                         // handle to object to close

if (!fSuccess)
      Label9->Caption = "CloseHandle(): Failed";
else
      Label9->Caption = "CloseHandle(): Passed";

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LVL 4

Expert Comment

by:md041797
ID: 1164037
Use the overlapped feature.  This will read as many chars as have arrived, return immediately, and it will report the count.  You can then assemble your records in a queue and pull them out when they are complete.
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