Com Port doesn't work unless Hyperterminal Open and Closes Port First

0
votes

So I am trying to connect to a piece of hardware. If I connect and disconnect with hyperterminal first. Then close the connection and the program. Everything works fine. If I don't I receive random characters back from the hardware. I use the same settings in hyperterminal as I do in the code.

baud=9600

parity=n

data=8

stop=1

Hardware flow controls "ON":

octs=on to=on dtr=on rts=hs

If I then disconnect the hardware and the serial port I will have the same problem again.

Is there anyway I can see how to comport is being configured after hyperterminal open and closes the port? I should note I am using a prolific serial to USB adapter.

Below is the code I use to open the com port. 

Function OpenCom(PortNum As Integer, Baud As Long) As Long

Dim lpDCB As DCB
Dim ComTimeout As COMMTIMEOUTS

com$ = "COM" + Trim(Str(PortNum))

'open the communications port
hcomtemp& = CreateFile(com$, GENERIC_READ Or GENERIC_WRITE, 0, ByVal 0, OPEN_EXISTING, 0, ByVal 0)

'check for errors
If hcomtemp& < 0 Then
    OpenCom = hcomtemp&
    Exit Function
End If
r& = PurgeComm(hcomtemp&, 12) ' purge the comm RX and TX (RXCLEAR=0x08 and TXCLEAR=0x04)
' COMMAND LINE for "Hardware" flow control - mode com: baud=9600 parity=n data=8 stop=1 octs=on to=on dtr=on rts=hs
  Build$ = "baud=" + Trim(str(Baud)) + " parity=N data=8 stop=1 octs=on to=on dtr=on rts=hs"

'build the data communications block
r& = BuildCommDCB(Build$, lpDCB)

'set the communications port's parameters with the DCB
r& = SetCommState(hcomtemp&, lpDCB)

ComTimeout.ReadIntervalTimeout = 100       'maximum time to wait between received bytes (milliseconds)
ComTimeout.ReadTotalTimeoutConstant = 1000  'maximum time to wait for receive data (milliseconds)

'set the timeouts
r& = SetCommTimeouts(hcomtemp&, ComTimeout)

'set the input buffer size to 4096 bytes and the output buffer size to 4096 bytes
r& = SetupComm(hcomtemp&, 4096, 4096)

'return the handle of the newly opened communications port
OpenCom = hcomtemp&

End Function
3
vbaexcelvbscriptvb6serial-port

3 Answers

1
votes

Please, try Advanced Serial Port Monitor -> Spy mode. http://www.aggsoft.com/serial-port-monitor.htm. It will show all actions that Hyperterminal does on the port. Then you can repeat these settings. It seems that the problem is related with the hardware flow control settings.

1
votes

Below is the code I used to fix my problem. I only ever had to do it this way for one piece of equipment. 

Function HandShakeBM5AS(ComPort As Integer) As Boolean

    Dim Bm5ACom As Long

        Dim x As Variant
        Dim Path As String
    comm$ = ComPort
    Commands$ = "MODE COM" & comm$ & ": BAUD=9600 PARITY=N DATA=8 STOP=1 TO=ON XON=OFF ODSR=OFF OCTS=ON DTR=ON RTS=HS IDSR=OFF"
    Call Shell("cmd.exe /S /C" & Commands$, vbNormalFocus)
    'Shell (Commands$)

    End Function
1
votes

BuildCommDCB() fails if 'rts=hs' is included in the control string. This causes lpDCB to be not set correctly, and SetCommState is called with the wrong values.

You can set the RTS control flag in the lpDCB structure after calling BuildCommDCB. (I would include code but I'm not certain on the Basic syntax)