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

Page 125

8M. Data Transfers

II. SOFTWARE GUIDES - 8. Driver488/DRV

II-110

Personal488 User’s Manual, Rev. 3.0

transfer, and when the

EOL

input terminator is set to

NONE

, Driver488/DRV does not append any

characters to the returned data.

Driver488/DRV senses the

EOL

output terminator to detect the end of a command or, in the case of the

OUTPUT

data command, to detect the end of the data. Most commands have many different variations.

It is the

EOL

output terminator that lets Driver488/DRV know when the command has been completely

received and is ready for execution. Without the

EOL

output terminator, there would be no way of

determining when one command ends and the next begins.

Driver488/DRV provides the

EOL

input terminator to the user’s program so that the program is able to

detect the end of a response. For example, BASIC needs to receive a carriage-return and line-feed
combination when using the

INPUT

statement to receive a response from Driver488/DRV.

Driver488/DRV automatically provides this EOL input terminator to the program.

For most programming languages, in most situations, both input and output

EOL

terminators should be

carriage-return line-feed (

CR LF

). These are the default values set up by

INSTALL

, but they can be

changed by using the

INSTALL

program. The

EOL

output terminator should be set to whatever is

conventionally sent at the end of a

PRINT

or equivalent statement to Driver488/DRV, and the

EOL

input terminator should be set to whatever is required at the end of a line of input from
Driver488/DRV.

As mentioned previously, the

EOL

output terminator is used to delimit the data portion of an

OUTPUT

command. If, in the

OUTPUT

command, no character count is specified, the

EOL

output terminator does

delimit data. However, if a character count is specified, Driver488/DRV will accept exactly that
number of characters from the program for output to the bus, even if the

EOL

output terminator is

among those characters. Furthermore, if a character count is not specified, the

TERM

output terminator

will be sent to the bus devices after the data. If a character count is specified, nothing will be sent to
the bus except the exact characters that were sent from the program. For example:

PRINT#1,"OUTPUT10;ABC"

sends

ABC

to device

, while

PRINT#1,"OUTPUT10#5;DEF"

sends

DEF

to device

because BASIC will send a carriage return and line feed

(

) at the end of the command, and a character count of

was specified.

The

EOL

input terminator delimits character strings returned to the program by Driver488/DRV.

However, if the character count is specified in an

ENTER

command, then exactly that number of

characters, without the

EOL

input terminator appended, will be returned to the program. In this case,

the normal

INPUT

statement will not be able to read the data from Driver488/DRV. Instead, a function

INPUT$(count,file)

that reads a specific number of characters, must be used. For example,

the following statements :

PRINT#1,"ENTER 16"
INPUT#2,A$

read a line of data from device

, while the following :

PRINT#1,"ENTER 16#10"
A$=INPUT$(10,2)

statements read exactly

characters from device

. Finally, the

EOL

terminators are not used in

BUFFERED

transfers, either

ENTER

OUTPUT

EOL IN NONE

As mentioned above, the input or output

EOL

terminators may be set to

NONE

. To understand how

communication with Driver488/DRV is possible without terminators, it is necessary to understand in
more detail how programs communicate with Driver488/DRV.

When a program sends information to Driver488/DRV, it uses an MS-DOS

Write Data

command. It

tells DOS where to send the data (to Driver488/DRV), the number of characters to send (from