LabVIEW
VISA Ethernet TCPIP (Socket) Termination Character
@RavensFan wrote:The proper situation is for the programmer to explicitly put the termination character at the end of the command if he needs one. That is not a workaround. If I'm sending anything by serial, or TCP/IP, I don't want VISA in the background adding any characters to the end of the message I send. Perhaps what I send in one command is just the first part of a longer message. If I want a character sent, I'll put it in there. If I don't, I don't want one added automatically.
I will also add that some instruments actually want 2 termination characters (Carriage Return AND a Line Feed). The VISA append can only add 1 character. So that is another argument that you should be handling your termination characters yourself.
@RavensFan wrote:I don't know much about GPIB and what end of message signals it uses...
GPIB has an EOI line to signal the end of a message. But most instruments I used still wanted the termination character(s).
The 488.2 standard mandates the use of the EOI line on the GPIB bus. Somewhere around the first half of 1990ies this became the default standard for new devices.
Older devices especially from HP insisted on using a termination character though, which is kind of funny considering that HP made the initial design of the HPIB bus, which later became the GPIB standard, and which contained the EOI line right from start already.
And while the Serial Port Initialization VI has read on termination character set to true on default this is a (convinient) utility function. The underlaying VISA session did at least in some distant past not automatically have this enabled for newly opened ASRL sessions.
And I’m with crossrulz on this: automatic termination character appending on write is a bad idea. All devices I have encountered which supported serial or ethernet connectivity did also support an optional termination character when communicating over GPIB so there was never a need to distinguish between the session type for the purpose of message termination, just append the termination characters to any message send, irrespective of the session type!
The property to automatically change the termination indication on write is a ASRL class specific property.
The higher Message class based property "Send End Enable" only enables the End on Write processing that will enable whatever the according ASRL class property specified. For non-ASRL it only enables:
On GPIB, VXI, GPIB-VXI, TCP/IP Instr, and USB Instr sessions, if this property is set to TRUE, VISA includes the 488.2 defined end of message terminator.
Now it seems almost impossible to find any specific document that actually lists what this 488.2 defined end of message terminator actually is for the various instruments!
I know that for GPIB it is the <LF> + EOI but no idea what it is for the others.
So yes those drivers are basically GPIB and RS-232 compatible only! Back around 2000 and before that, it was not that crazy of a choice, although I told people already then to not rely on that feature but instead create the command strings with explicitly appended termination character.
A quite common response back then was: It works that way, so why bother!!
Pretty much all but the most obscure GPIB devices simply accept commands with a termination character too. Before the 488.2 standard was created, many HP devices actually required it, despite that the GPIB bus created by them had a specific EOI signal line for that purpose.
