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

Page 89

8H. Turbo C

II. SOFTWARE GUIDES - 8. Driver488/DRV

II-74

Personal488 User’s Manual, Rev. 3.0

Driver488/DRV can accept commands only when it is in a quiescent, ready state. While
Driver488/DRV should normally be ready, it is possible that it was left in some unknown state by a
previous program failure or error. In order to force Driver488/DRV into its quiescent state, we use the

IOCTL_WT

function:

ioctl_wt(ieee,"break",5);

This

IOCTL_WT

function is equivalent to the BASIC statement

IOCTL#1,“BREAK”

which sends the

BREAK

command through a “back door” to Driver488/DRV. Driver488/DRV recognizes this “back

door” command regardless of what else it might be doing and resets itself so that it is ready to accept a
normal command. We can then completely reset the Driver488/DRV with the

RESET

command:

ieeewt(“reset\r\n”);

which resets the operating parameters of the Driver488/DRV back to their normal values (those that
were set during system boot by the

DRVR488

DOS command). Notice that the

EOL OUT

terminators

that mark the end of a Driver488/DRV command are reset to carriage return and line feed by the

IOCTL_WT

command. Thus, the

RESET

command must be terminated by both a carriage return (

)

and a line feed (

). As it is more convenient if Driver488/DRV accepts line feed only as the

command terminator, we use the

EOL OUT

command to set the command terminator to line feed (

ieeewt(“eol out lf\r\n”);

Notice that this command must also be terminated by both a carriage return and a line feed because the
command terminator is not changed until after the

EOL OUT

command is executed.

Character strings in C are normally terminated by a null (an

ASCII 0

). Thus, it is appropriate for

Driver488/DRV to terminate its responses to the program with a null so that the response can be treated
as a normal character string. We can use the

EOL IN

command to configure Driver488/DRV so that it

does provide an ASCII null terminator:

ieeewt(“eol in $0\n”);

Finally, we enable

SEQUENCE - NO DATA AVAILABLE

error detection by setting the

FILL

mode to

ERROR

ieeewt(“fill error\n”);

All the commands discussed so far:

OPEN

RAWMODE

IOCTL_WT

RESET

EOL OUT

EOL IN

and

FILL

ERROR

are part of the

IEEEINIT

function included in

IEEEIO.C

IEEEINIT

returns a zero if these

steps were executed successfully, and a

-1

if some error was encountered. Thus, to accomplish all the

above steps, we just use the following:

#include “ieeeio.h”
#include .h
if (ieeeinit() == -1) {
printf(“Cannot initialize IEEE system.\n”);
exit(1);
}

The two

INCLUDE

statements provide the program with definitions of the standard I/O and IEEE I/O

functions so they can be referenced by the demo program.

IEEEINIT

is called to initialize the system,

and if it indicates an error (returns a

-1

), we print an error message and exit. If there was no error, we

just continue with the program.

Once everything is reset, we can test the communications and read the Driver488/DRV revision number
with the

HELLO

command:

char response[256];
ieeewt(“hello\n”);
ieeerd(response);
printf(“%s\n”,response);

We first

IEEEWT

the

HELLO

command, then

IEEERD

the response from Driver488/DRV into the

character string response (

IEEEWT

and

IEEERD

are both supplied in

IEEEIO.C

). Finally, we display

the response with a

PRINTF