Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 308)

III. COMMAND REFERENCES - 15. Command References 15A. Driver488/DRV Commands
Personal488 User’s Manual, Rev. 3.0 III-293
selects which response is to be used. In general, when Driver488 receives a request for data, it is
provided with the address in memory of a buffer that is to hold the response, and with the buffer length.
If FILL OFF is specified, then the buffer is filled with any available response, and the remainder of the
buffer (if it is larger than the response) is not changed. If no response is available, then the entire
buffer is left unchanged, but no error is indicated.
If FILL ERROR is specified, then the buffer is filled with any available response, and the remainder of
the buffer (if it is larger than the response) is not be changed. If no response is available, then the
entire buffer is left unchanged and a
SEQUENCE - NO DATA AVAILABLE error occurs.
If FILL term is specified, where term is one of CR , LF , $char , or ‘X , the buffer is filled with any
available response, and the remainder of the buffer (if it is larger than the response) is filled with the
specified character. If no response is available, the entire buffer is filled with that character.
If the error is due to an actual programming error, it is to the user’s advantage to have Driver488
automatically detect this error. In this case, error detection should be enabled with the
FILL ERROR
command. Normal I/O with Driver488 in both BASIC and Turbo Pascal 3.0 is performed on a
character-by-character basis and so neither language reads more data than is available. Thus,
FILL ERROR is appropriate for both languages. Note, however, that the OPEN for input command in
some versions of BASIC does try to read one character upon opening the file. For this reason, the files
should be opened in the following sequence:
100 OPEN “\DEV\IEEEOUT” FOR OUTPUT AS #1
110 IOCTL#1,"BREAK"
120 PRINT#1,"RESET"
130 OPEN “\DEV\IEEEIN” FOR INPUT AS #2
140 PRINT#1,"FILL OFF"
The RESET command guarantees that FILL$000 (the default condition, FILL with the null character) is
in effect when the OPEN statement tries to read the first character from Driver488. Driver488 responds
with a null character that BASIC ignores so that the first real response from Driver488 will be
corrupted.
In some languages, such as C, the I/O routines may try to read a fixed length block from Driver488.
Use of the BASIC
GET file I/O also has this effect. The size of the block requested varies. It may be as
much as several thousand bytes, or it may be the record size or buffer length defined for the file. In any
case, if
FILL is OFF , then no error is signaled, and the returned characters are placed into the first bytes
of the buffer. The remainder of the block is not modified. It is, though, sometimes useful to fill the
remainder of the block with some specific byte value. This is accomplished with the
FILL term
command. FILL term forces Driver488 to return as many characters as are requested by the I/O
routines, even if they are dummy fill characters.
FIND LISTENERS
SYNTAX FIND LISTENERS pri-addr
RESPONSE The number of active listeners found, followed by those
addresses, separated by commas.
MODE Any
BUS STATES UNL, LAG
SEE ALSO CHECK LISTENER, BUS ADDRESS, STATUS
EXAMPLES PRINT#1,"FIND LISTENERS 12"
LINE INPUT#1,A$
0 No Listeners Found
1,12 Primary Address Listener Found
2,1200,1201 Secondary Address Listeners Found
The FIND LISTENERS command finds all of the devices configured to listen at the specified primary
address on the IEEE 488 bus. It takes the primary address to check, and returns the number of listeners
found and their addresses.