Using RS-232 Device Sessions

An RS-232 device session allows direct access to a device, regardless of the type of interface to which the device is connected. The specifics of the interface are hidden from the user.

This topic provides an overview of RS-232 interfaces, including typical hardware configuration, using the Connection Expert utility, and an example of a configuration using SICL.

The subtopics are:

• Addressing an RS-232 Device
• SICL Functions for RS-232 Device Sessions
• Device Session Sample Programs
  • Sample: RS-232 Device Session (C)
  • Sample: RS-232 Device Session (Visual Basic) (Windows only)

Addressing an RS-232 Device

To create a device session, specify the interface logical unit or symbolic name, followed by a device logical address of 488. The device address of 488 tells SICL that communication is with a device that uses the IEEE-488.2 standard command structure.

For other interfaces (such as GPIB), SICL supports the concept of primary and secondary addresses. However, for RS-232, the only primary address supported is 488. SICL does not support secondary addressing on RS-232 interfaces.

NOTE: If a device does not “speak” IEEE-488.2, you can still use SICL to communicate with the device. However, some SICL functions that work only with device sessions may not operate correctly. See SICL Functions for RS-232 Device Sessions for details.

The interface logical unit and symbolic name are defined by running Connection Expert.

Some example addresses for RS-232 device sessions:

COM1,488
serial,488

Examples of opening a device session with an RS-232 device:

C sample:

INST dmm;
dmm = iopen (“com1,488”);

Visual Basic sample:

Dim dmm As Integer
dmm = iopen (“com1,488”

SICL Functions for RS-232 Device Sessions

This section describes how some SICL functions are implemented for RS-232 device sessions. There are specific device session interrupts that can be used.

SICL Functions for RS-232 Device Sessions

Function	Description
iprintf, iscanf, ipromptf	SICL’s formatted I/O routines depend on the concept of an EOI indicator. Since RS-232 does not define an EOI indicator, SICL uses the newline character (\n) by default.   You cannot change this with a device session. However, you can use the iserialctrl function with an interface session. See in this topic for details.
ireadstb	Sends the IEEE 488.2 command *STB? to the instrument, followed by the newline character (\n). It then reads the ASCII response string and converts it to an 8-bit integer. This will work only if the instrument understands this command.
itrigger	Sends the IEEE 488.2 command *TRG to the instrument, followed by the newline character (\n). This will work only if the instrument understands this command.
iclear	Sends a break, aborts any pending writes, discards any data in the receive buffer, resets any flow control states (such as XON/XOFF), and resets any error conditions. To reset the interface without sending a break, use: iserialctrl (id, I_SERIAL_RESET, 0)
ionsrq	Installs a service request handler for this session. Service requests are supported for both device sessions and interface sessions. See SICL Functions for RS-232 Device Sessions in this topic for details.

Device Session Sample Programs

This section contains two sample programs for RS-232 interface device session programming.

Sample: RS-232 Device Session (C)

This sample program takes a measurement from a DVM using a SICL device session. This sample program was tested with a 34401A digital voltmeter. When you run the program with a serial connection to the 34401A, be sure that DTR/DSR flow control is set for the serial port. Otherwise, the program will appear not to work.

/* ser_dev.c
This example program takes a measurement from a DVM using a SICL device session.*/

#include <sicl.h>
#include <stdio.h>
#include <stdlib.h>

#if !defined(WIN32)
#define LOADDS __loadds
#else
#define LOADDS
#endif

void SICLCALLBACK LOADDS error_handler (INST id,
int error) {

printf (“Error: %s\n”, igeterrstr (error));
exit (1);
}

main()
{
INST dvm;
double res;

/* Log message and terminate on error */
ionerror (error_handler);

/* Open the multimeter session */
dvm = iopen (“COM1,488”);
itimeout (dvm, 10000);

/* Prepare the multimeter for measurements */
iprintf (dvm,”*RST\n”);
iprintf (dvm,”SYST:REM\n”);

/* Take a measurement */
iprintf (dvm,”MEAS:VOLT:DC?\n”);

/* Read the results */
iscanf (dvm,”%lf”,&res);

/* Print the results */
printf (“Result is %f\n”,res);

/* Close the voltmeter session */
iclose (dvm);

/* This call is a no-op for WIN32 programs */
_siclcleanup();

return 0;
}

Sample: RS-232 Device Session (Visual Basic)

This sample program takes a measurement from a DVM using a SICL device session. This sample program was tested with a 34401A digital voltmeter. When you run the program with a serial connection to the 34401A, be sure that DTR/DSR flow control is set for the serial port. Otherwise, the program will appear not to work.

Option Explicit
'''''''''''''''''''''''''''''''''''''''''''''''
' ser_dev.bas
' This example program takes a measurement from
‘ a DVM using a SICL RS-232 device session.
'''''''''''''''''''''''''''''''''''''''''''''''

Sub Main()

Dim dvm As Integer
Dim res As Double
Dim argcount As Integer

' Open the multimeter session
' "COM1" is the SICL Interface name as defined
‘ in Connection Expert
' Change this to the SICL name you have defined
dvm = iopen("COM1,488")

' Set timeout to 10 sec
Call itimeout(dvm, 10000)

' Prepare the multimeter for measurements
argcount = ivprintf(dvm, "*RST" + Chr$(10),
0&)
argcount = ivprintf(dvm, "SYST:REM" +
Chr$(10), 0&)

' Take a measurement
argcount = ivprintf(dvm, "MEAS:VOLT:DC?" +
Chr$(10))

' Read the results
argcount = ivscanf(dvm, "%lf", res)

' Print the results
MsgBox "Result is " + Format(res),
vbExclamation

' Close the multimeter session
Call iclose(dvm)

' Tell SICL to cleanup for this task
Call siclcleanup

End Sub