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

Page 93

8H. Turbo C

II. SOFTWARE GUIDES - 8. Driver488/DRV

II-78

Personal488 User’s Manual, Rev. 3.0

Once we have enabled interrupt checking by setting

IEEE_CKI

to point to

CKLPINT

, and specified the

interrupt service routine by setting

IEEE_ISR

to point to

isr

, then we can specify which conditions are

to cause an interrupt. The

ARM

command specifies those conditions. In this example we want the

interrupt to occur on the detection of a Service Request (

SRQ

ieeewt(“arm srq\n”);

The 195 can be set to request service on any of several different internal conditions. In particular, the

command causes an

SRQ

on the detection of any invalid command or command option by the 195:

ieeewt(“output 16;M2X”);

This

OUTPUT

command is placed early in the program so that all subsequent commands to the 195

cause an

SRQ

, if they are invalid.

Now that interrupt detection is enabled, and the interrupt service routine is specified, we must specify
the actions to take to service the interrupt. We first display a message indicating that an interrupt was
detected, and then turn off interrupt checking:

void isr()
{ int _false()_;
printf(“Interrupt detected...”);
ieee_cki = _false_;

We next check the Driver488/DRV Serial Poll Status to determine if an

SRQ

actually caused the

interrupt:

int sp;
ieeewt(“spoll\n”);
ieeescnf(“%d”,&sp);
if (sp==0) {
printf(“Non-SRQ Interrupt!\n”);
exit(1);
}

We then Serial Poll the 195 to determine its status. If there were other devices on the bus that could be
generating the

SRQ

, each of them would be have to be checked in turn.

int st195;
ieeewt(“spoll 16\n”);
ieeescnf(“%d”,&st195);
if ((st195 & 0x40) == 0 ) {
printf(“Non-195 SRQ!\n”);
exit();
}

Bit

DIO7

, with a value of

0x40

, is returned as true (

) in the Serial Poll response of those devices

requesting service. In our simple example we expect that the 195 is the only possible cause of an

SRQ

and if not, there must be some error.

Now that we have identified the device that is requesting service, we can further examine the Serial
Poll status to classify the request:

if ((st195 & 0x20) == 0) {
if (st195 & 0x01)
printf(“Overflow\n”);
if (st195 & 0x02)
printf(“Buffer Full\n”);
if (st195 & 0x04)
printf(“Buffer 1/2 Full\n”);
if (st195 & 0x08)
printf(“Reading Done\n”);
if (st195 & 0x10)
printf(“Busy\n”);
} else {
if (st195 & 0x01)
printf(“Illegal Command Option\n”);
if (st195 & 0x02)