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

Page 70

II. SOFTWARE GUIDES - 8. Driver488/DRV

8E. Microsoft C

Personal488 User’s Manual, Rev. 3.0

II-55

Also, in Microsoft C and Turbo C, the file must be opened in

BINARY

mode so that end-of-line

characters are not translated.

In Microsoft C and Turbo C, the file is opened with the following statement:

ieee=open(“ieee”,O_RDWR | O_BINARY);

which is part of the

IEEEINIT

function contained in

IEEEIO.C

supplies several other

useful routines and definitions. These routines and definitions are described later in more detail in
“Interrupt Handling,” an upcoming topic in this Sub-Chapter.

In the above statement, the value returned by

OPEN

and placed into the integer variable

IEEE

, is either

the handle of the opened file, or

-1

if some error has occurred. The

IEEEINIT

routine checks for this

error indication and returns a

-1

if there has been such an error.

Of course, the file descriptor variable name

IEEE

may be changed as desired, but throughout this

manual and the program files,

IEEE

has been used. Once the file is opened, we can send commands

and receive responses from Driver488/DRV.

Normally, when DOS communicates with a file, it checks for special characters, such as

control-Z

which can indicate end-of-file. When communicating with IEEE 488 devices, DOS’s checking would
interfere with the communication. The

RAWMODE

function prevents DOS from checkings for special

characters:

rawmode(ieee);

As an additional benefit, communication with Driver488/DRV is much more efficient when DOS does
not check for special characters.

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 just 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”);