How to detect a serial printer programmatically?

[AJ_CS]

I have a serial printer connected to COM Port.

Is it possible to check if it is connected, programmatically?

I tried 'VISA find resources' function, but it always lists the COM port whether the printer is connected or not.

[GerdW]

Hi AJ,

can you send a command to your printer and check for the devices answer? That would be a presence test...

[paul_a_cardinale]

Functions -> Report Generation -> Advanced Report Generation -> Query Available Printers

[Dennis_Knutson]

I'm not sure the report generation function will work in all cases. It reads the printers that are configured and the default printer. I just ran it and it returned a list including a network printer to a disconnected network.

[mikeporter]

What kind of printer is it?

Mike,,,

[AJ_CS]

The printer is 'Star DP8340' serial printer. It is connected to the COM1 port through DB9 connector.

I tried to communicate to the device using VISA. But it returned following error.

BUt I am able to print from MS office as well as Labview report generation.

The VISA configuration details such as port name and baud rate are correct, I collected it from the windows printer port configuration. But for some reason, the Labview VISA is unable to communicate.

[mikeporter]

Ok, I think that the problem is that the OS sees a printer on that com port.

You get the error because you are trying to talk to a serial device on COM1 but the OS is saying you can't do that because there's a printer there. In essence, the com port is tied up or busy because the OS is using to communicate with a printer.

Mike...

[AJ_CS]

Ok, does that mean it is not possible to detect the printer programmatically?

[rolfk]

Most likely not easily!

LabVIEW can not access the printer since its port is likely already reserved/opened by the printer driver. VISA actually has a specific error code for ports that are normally opened by another process but the error message is a little unspecific. But most likely the printer driver has reserved the port in some non-standard way and VISA then gets some unexpected error because of that.

And the Windows API doesn't have a simple way to query the state of a printer other than if it is installed or not. An involved way may work, using EnumPrinters() requesting for PRINTER_INFO_2 data and checking the Status element in every returned printer record for the PRINTER_STATUS_OFFLINE flag, but that API doesn't count as easy to interface with the Call Library Node.

[sebster]

I looked at the manual for your printer and on page 17 (actually page 21 of the document) is the following information on Control Codes:

CODE ENQ (05)H

FUNCTION Enquiry

OUTLINE

When this code is received, the printer outputs status data.

If it is input after text data input in the STX-ETX mode, the

printer outputs status data and the check byte.

I don't have access to this printer (or any other similar models) to try this out but could this be of any use to you?