Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi User Manual

Page 253

10F. Visual Basic

II. SOFTWARE GUIDES - 10. Driver488/W31

II-238

Personal488 User’s Manual, Rev. 3.0

When the IEEE 488 Event Custom Control has been placed in your application, the following service
routine is made available. The particular subroutine is invoked when the ADC generates an

SRQ

“acquisition complete”.

Sub Event4881_Srq ()

‘Clear SRQ condition
rv% = spoll (adc)

‘Reset the buffer pointer of the ADC488
rv% = ioOutput (adc, “B0X”)

‘Get 100 readings from the ADC488
TextWindow.Text = “”
For i% = 1 to 100

rv% = Enter(adc, response)
TextWindow.Text = TextWindow.Text + response

Next i%

End Sub

The sole button on the form opens the pre-configured ADC then initializes it by clearing it. Next, the
IEEE 488 event handling is setup by affiliating the

Handle

property of the

Event4881

control to the

newly opened ADC handle. For the bus event to be captured and sent to the custom control, the ADC
handle must be left open.

Sub Command1_Click ()

‘Now opening a device named ADC
adc = OpenName (“ADC”)
If (adc = -1) Then

MsgBox “Cannot initialize device ADC”
End

End If

To activate this event (

SRQ

), the

SRQ

property of the IEEE controller must be set to

True

. At design-

time, select the IEEE 488 tool icon on your form, then select

SRQ

in the properties area. Set the

SRQ

property to

True

Note that upon closing the handle, all event handling associated with this control is disabled. You must
keep the device open during the time in which its events are of interest. That is, with an ADC488, you
would open the device, assign the handle to the Event Custom Control’s

Handle

property, configure

the

adc

with

ioOutput

commands, and then wait for the

SRQ

event to be triggered. The

SRQ

event

handler would read data from the ADC488 and then close the device, allowing other tasks access, and
eliminating the event notification. The data read from the ADC488, is displayed in the Driver488/W31
Custom Control Example window, as shown in the figure.

Data read from the ADC488