IEEE-488 PROGRAMMING
and return it to its power-up default conditions. Note that
the DCL command is not an addressed command, so all
instruments equipped to implement DCL will do so
simultaneously. When the Model 263 receives a DCL com-
mand, it will return to the power-up default conditions.
To send the DCL command, the controller must perform
the following steps:
1. Set ATN true.
2. Place the DCL command byte on the data bus.
HP-85 Programming Example-Place the unit in an
operating mode that is not a power-up default condition.
Now enter the following statement into the computer
keyboard:
CLEAF: ;
When the END LINE key is pressed, the instrument
returns to the power-up default conditions.
4.6.6 SDC (Selective Device Clear)
The SDC command is an addressed command that per-
forms essentially the same function as the DCL command.
However, since each device must be individually ad-
dressed, the SDC command provides a method to clear
only a single, selected instrument instead of clearing all
instruments simultaneously, as is the case with DCL.
When the Model 263 receives the SDC command, it will
return to the power-up default conditions.
To transmit the SDC command, the controller must per-
form the following steps:
1. Set ATN true.
2. Address the Model 263 to listen.
3. Place the SDC command on the data bus.
HP-85 Programming Example-Place the unit in an
operating mode that is not a power-up default condition.
Now enter the following statement into the computer
keyboard:
After END LINE is pressed, the instrument returns to the
power-up default conditions.
4.6.7 SPE, SPD (Serial Polling)
The serial polling sequence is used to obtain the Model
263 serial poll byte. The serial poll byte contains irnpor-
tant information about internal functions, as described in
paragraph 4.7.9. Generally, the serial polling sequence is
used by the controller to determine which of several in-
struments has requested service with the SRQ line.
However, the serial polIiig sequence may be performed
at any time to obtain the status byte from the Model 263.
The serial polling sequence is conducted as follows:
1. The controller sets ATN true.
2. The controller then places the SPE (Serial Poll Enable)
command byte on the data bus. At this point, all ac-
tive devices are in the serial poll mode and waiting to
be addressed.
3. The Model 263 is then addressed to talk.
4. The controller sets ATN false.
5. The instrument then places its serial poll byte on the
data bus, at which point it is read by the controller.
6. The controller then sets ATN true and places the SPD
(Serial Poll Disable) command byte on the data bus to
end the serial polling sequence.
Once instruments are in the serial poll mode, steps 3
throu
talk i
h 5 above can be repeated by sending the correct
a dress for each instrument. ATN must be true when
the address is transmitted and false when the status byte
is read.
HP-85 Programming Example-The SPOLL statement
automatically performs the sequence just described. To
demonstrate serial polling, enter in the following
statements into the computer:
When the END LINE key is pressed the first time, the
computer initiates the serial polling sequence. The decimal
value of the serial poll byte is then displayed on the com-
puter CRT when END LINE is pressed the second time.
4-8
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