Syntax:
|
event OnRead(Data): HResult
|
Use OnRead event handler to implement asynchronous reading
from the communication ports. In the default (character)
mode, Data parameter has string type. If COM port
component was opened in the binary mode, this parameter is
an array of bytes. It should be emphasized that
asynchronous communications usually is a great problem since
you can't wait for your device finish to transmit all data
- for RS232 ports (and, to a greater extent, for TCP/IP
sockets) it can take seconds. At once, your application must
remain interactive while data are going.
Internally, reading data from "slow" ports
requires multithreading. From the component user's standpoint,
you must handle OnRead event. Keep in mind that data packet
from the device may be broken at the arbitrary position, so
that you should analyze incoming data and perform something
only when all data actually are ready. Usually you will rely
on special "terminator" characters as shown in the
example below:
Example:
Dim TCBuf ' allocate buffer for incoming data
Sub TCPort_OnRead(Str)
dim tctemp
TCBuf=TCBuf+Str ' accumulate incoming data in TCBuf
if (InStr(TCBuf, vbCrLf)>0) then ' terminator arrived?
tctemp=Mid(TCBuf, 2, 5) ' extract readout
if IsNumeric(tctemp) then ' check whether it is correct
' here you can safely process the device data
end if
TCBuf="" ' clear buffer
end if
End Sub
Notice: for objects with
IDMCPortLibX interface you may define Terminator
property in order to engage internal bufferization.
Syntax:
|
event OnError(Data): HResult
|
For serial communication port controls, this event fired
when some error condition is detected, typically when you are
trying to open port which is not exists or already opened by
other control or application. Data parameter may contain
a string that explains the reason of error.
IDMCPortLibXEvents interface should be used to receive notifications from
serial (RS232) communication ports controls. It is very important since RS-232
communication media have large delays (hundreds of milliseconds and even seconds),
so that data exchange is essentially asynchronous. Events allows you receive data
when they are ready, without wait.
