Measurement-computing Personal488 rev.3.0 For DOS & Windows 3.Xi Manuel d'utilisateur télécharger pdf (Page 77)

8E. Microsoft C II. SOFTWARE GUIDES - 8. Driver488/DRV

II-62 Personal488 User’s Manual, Rev. 3.0

receive buffer,

chars

. This means

chars

must be an array of known size, for example,

char chars[256]

, not

char*chars

•

IEEEPRTF

and

IEEESCNF

are IEEE 488 versions of

PRINTF

and

SCANF

, respectively.

int ieeeprtf(format,...)

char *format

int ieeescnf(format,a,b,c,d,e)

char *format,*a,*b,*c,*d,*e

The

IEEEPRTF

accepts a format string and a list of arguments. It formats its arguments according

to the specified format and sends the formatted string to Driver488/DRV. The

IEEESCNF

accepts

a format string and up to 5 pointers (to the types specified in the format string). It reads a string of

up to 256 bytes from Driver488/DRV, terminates it with a zero, converts it according to the format

string, and places the converted values into the variables pointed to by the specified pointers.

•

RAWMODE

sets the file specified by

handle

for “raw mode” I/O.

int rawmode(handle)

int handle

In “raw mode” MS-DOS does not interpret the characters received from the file. In particular,

control-Z

is not taken as end-of-file. “Raw mode” is usually appropriate for IEEE 488

communications because it does not interfere with the transfer of binary data and because it is

much more efficient than “non-raw mode” I/O.

•

IEEEINIT

establishes communications with Driver488/DRV and configures it for use with C.

int ieeeinit()

It first opens the file

IEEE

for both reading and writing and puts the file descriptor into

IEEE

. It

then puts the file into “raw mode”. Driver488/DRV is then initialized by sending the

IOCTL

“BREAK”

and

RESET

commands. Normal output from C is terminated by a new-line (line feed)

character, and returned strings should be terminated by a null, so

EOL OUT LF

and

EOL IN $0

commands are then issued. Finally a

FILL ERROR

command is issued to enable

SEQUENCE - NO

DATA AVAILABLE

error detection. If an error is detected during any of these commands,

IEEEINIT

returns a

-1

, otherwise it returns a zero (

CRITERR.ASM (Microsoft C & Turbo C)

Normally, when Driver488/DRV detects an error, perhaps due to a syntax error in a command, it

responds with an I/O error to DOS. When this happens, DOS normally issues an

ABORT

RETRY

IGNORE

message and waits for a response from the keyboard. There is no way for the user’s program

to detect such an error, determine the cause, and take appropriate action. However, DOS does provide

a method of redefining the action to be taken on such a “critical error”.

CRITERR.ASM

contains a

critical error handler that, when invoked, makes it appear to the calling program that some less-critical

error has occurred. The critical error handler is installed by

CRIT_ON()

and removed by

CRIT_OFF()

.The critical error handler is also automatically removed by DOS when the program exits.

The following program fragment demonstrates the use of the critical error handler:

#include “criterr.h”

crit_on(ieee);

if (ieeewt(“output 16;F0X”) == -1) {

printf(“Error writing F0X to device 16, \n”);

crit_off();

ioctl_wt(ieee,"break",5);

ieeewt(“eol out lf\r\n”);

ieeewt(“status\n”);

ieeerd(response);

printf(“status = %s\n”,response);

crit_on(ieee);

}

We must first

#include

the header file with the definitions of the critical error routines. We then

enable critical error trapping with

CRIT_ON

which takes as a parameter the handle of the file for which

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Measurement-computing Personal488 rev.3.0 For DOS & Windows 3.Xi Manuel d'utilisateur Page 77

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