DM SerialControl Communication - serial-port

Question

Running this script in DM results in the following error during the first execution. Subsequent executions fail on SPOpen(1,9600,1,0,8), which I think implies the serial port is open at that point, but the first execution says it is not.
What is the unexpected error that is preventing communication with the serial port?
SPOpen(1,9600,1,0,8)
SPOpen( "COM1" )
SPSendString(1, "*IDN?" )
string message
number test
message = SPReceiveString(1,8,test)
Result("Acquisition "+message+" "+test+"\n")
SPClose(1)

Answer 1

I can't test the serial commands myself at the moment, and the exact script code of course depends on what is on the other end of the serial connections, i.e. what is expected and what is send back. And also what timeouts/delays need to be expected and cared for.
However, I can see two immediate issues with your script:
The 'SPOpen()' command returns an ID value. You need this ID in the subsequent commands, not the port number.
Whenever the script fails (i.e. throws and error), the command to close the port is never executed and it remains open (and hence blocked). To safeguard against this, you can use a 'Try{}Catch{}' construct.
I would expect your script to look something more akin to the following:
number port = 666
number baud = 9600
number stop = 10
number parity = 0
number data = 8
number portID
try
{
portID = SPOpen( port, baud, stop, parity, data )
Result( "\n Port ("+port+") opened, Handle ID: " + portID )
Result( "\n Sending messge:" + message )
string message = "*IDN?"
SPSendString( portID, message )
Result( "\n messge send." )
// Wait for response
Result( "\n Waiting for response." )
sleep( 0.3 )
number pendingBytes = SPGetPendingBytes(portID)
Result( "\n Pending bytes:" + pendingBytes )
number maxLength = 50
number bytes_back
string reply
while( pendingBytes > 1 )
{
reply += SPReceiveString( portID, maxLength, bytes_back )
pendingBytes = SPGetPendingBytes(portID)
}
Result( "\n Reply:" + Reply )
}
catch
{
// Any thrown error end up here.
// Ensures the port will not remain open
Result( "ERROR OCCURRED.\n" )
break
}
SPClose( portID )
Result( "\n Port ("+port+") closed, using Handle ID: " + portID )
The above is untested code and will surely require some adaptation, but it should get you started. You might need some "delays" when waiting for a result and you might want to wait for specific results in a while-loop.