String Literals

The first 'HelloWorld' is a literal -ASCII

The second "HelloWorld'" is a pre-defined variable

The first command will work if it is all you want to send but if you want to add a variable with it, then you must use the " ". It's good practice to ALWAYS use the " " in all command like:

SEND_STRING someDevice, " 'Hello World' "

with VARIABLE:
SEND_STRING someDevice, " 'Hello World', someVAR"

Hope this helps!

You will need to be a little carefull when dealing with variables in Netlinx as some may operate differently depending on the section of code you are in. Learned this the hard way. Here's a sample:

DEFINE_CONSTANT
CHAR EF_2280[] = 'F01'
CHAR PGM_VOLUME_UP[] = "EF_2280,'MACROX4'"

BUTTON_EVENT[dvTPANEL,51]
{
PUSH:
{
SEND STRING dvA_CONF,"PGM_VOLUME_UP"
}
}

it ended up sending "EF_2280,'MACROX4'" out of the RS-232 port.

Assigning CHAR PGM_VOLUME_UP[12] in the DEFINE_VARIABLE section instead, and then adding the statement PGM_VOLUME_UP = "EF_2280,'MACROX4'" in the DEFINE_START section fixed the issue and sent "F01MACROX4".
Have not researched further why this is the case, but I have become very careful with strings in the DEFINE_CONSTANT section.