read from serial port

[wong]

Hi,i am using serial communication to read from a plc.The plc will send a string :&H3A as a header byte then C(which is a variable that contains data)I want to read and mask out the header byte.I use the following code but cannot read anything.Any suggestions?

Private Sub btnread_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnread.Click
Msg = SerialPort1.ReadExisting
count = Val(Mid(Msg, 3, 2))

Lblno.Text = count
End Sub

[dbasnett]

what version of vb are you using? are you saying the device sends (in hex) this

3AC

[wong]

I am using vb.net 2005

The header byte &H3A is supposed to be ":"
and then it sends C which means i think it sends ":C"

[dbasnett]

what does "The header byte &H3A... " mean? does the device send on a periodic basis?

[wong]

Sorry but i am also not very sure about that but i think that the plc must send the header byte as to inform when the string starts.&H3A is like a short code for the simbol ":" And also if the plc does not send continuosly does it mean i must change the plc program to constantly send the string in order for my vb program to work?

[dbasnett]

you really need to know the protocol of the PLC device. if you need to interrogate the device or not, when it sends, what it sends, what it means, etc.

ascii codes