Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 220)

II. SOFTWARE GUIDES - 10. Driver488/W31 10C. External Device Interfacing
Personal488 User’s Manual, Rev. 3.0 II-205
Use of External Devices
When using subroutine Application Program Interface (API) functions, it is first necessary to obtain a
device handle for the device(s) with which you wish to interact.
When using Driver488/W31, the OpenName function must be the first function called in the program.
It takes the name of the device to open and returns a handle for the specified interface board or device.
Every other function can then use that handle to access the device.
The following program illustrates how Driver488/W31 might communicate with an analog-to-digital
converter (
adc ) and an oscilloscope ( scope ):
DevHandleT ieee; // handle to access the interface board ieee
DevHandleT adc; // handle to access a ADC488
DevHandleT scope; // handle to access the scope
DevHandleT deviceList[5]; // array containing a list of device handles;
int err;
Communication with a single device:
adc = OpenName (“ADC”);
If you use several devices, you must open each one.
ieee = OpenName(“IEEE”);
scope = OpenName(“SCOPE”);
// Add adc to the list of devices
deviceList[0] = adc; // Add oscilloscope to the list of devices
deviceList[1] = scope // End of list marker
deviceList[2] = -1;
Abort(ieee); // Send Interface Clear (IFC)
Output(scope,"SYST:ERR?"); // Read SCOPE error status
Enter(scope,data);
printf(data);
Output(adc,"A0 C1 G0 R3 T0 X"); // Set up ADC488
Enter(adc,data);
printf(data);
ClearList (deviceList) ; // Send a Selected Device Clear (SDC) to a list
Close (adc) ; // Close ADC488. Handle is now unavailable for
// access.
If we tried to call Output by sending the handle adc without first opening the name ADC , an error
would result and Output would return a -1 as shown below:
result = Output (adc, “A0 C1 G0 R3 T0 X”);
printf (“Output returned: %d.\n”,result);
should print:
Output returned: -1.
As mentioned above, named devices have another advantage: they automatically use the correct bus
terminators and time out. When a named device is defined, it is assigned bus terminators and a time
out period. When communicating with that named device occurs, Driver488/W31 uses these
terminators and time out period automatically. Thus
Term commands are not needed to reconfigure the
bus terminators for devices that cannot use the default terminators (which are usually carriage-return
line-feed
EOI ). It is still possible to override the automatic bus terminators by explicitly specifying the
terminators in an Enter or Output command, or to change them semi-permanently via the Term
command. For more information, see the Enter , Output , and Term commands described in
“Section III: Command References.”
Extensions For Multiple Interfaces
Driver488/W31 allows the simultaneous control of multiple interfaces each with several attached
devices. To avoid confusion, external devices may be referred to by their “full name” which consists of
two parts. The “first name” is the hardware interface
name , followed by a colon separator ( : ). The
“last name” is the external device name on that interface. For example, the “full name” of DMM might
be IEEE:DMM .