3.4.4 Unaddress Commands
purposes only; the Model 617 does not have secondary ad-
dressing capabilities.
The two unaddress commands are used by the controller to
remove any talkers or listeners from the bus. ATN is true
Note that these commands are normally transmitted with the
when these commands are asserted.
7 bit code listed in Figure 3-3. For many devices, the condition
of DI08 is unimmxtant. However. manv devices mav reouire
I
, .
that DI08 has a value of logic 0 (high) to properly send com-
UNL (LJnlisten)-Listeners are placed in the listener idle state
mands.
by the UNL command.
UNT (Untalk)-Any previously commanded talkers will be
Hexadecimal and decimal values for each of the commands or
placed in the talker idle state by the UNT command.
command groups are listed in Table 3-2. Each value assumes
that DI08 has a value of 0.
3.4.5 Device-Dependent Commands
Table 3-2. Hexadecimal and Decimal Command
Codes
The meaning of the device-dependent commands will depend
on the configuration of the instrument. Generally, these com-
mands are sent as one or more ASCII characters that tell the
device to perform a specific function. For example, the com-
mand sequence FOX is used to place the Model 617 in the volts
mode. The IEEE-486 bus actually treats these commands as
data in that ATN is false when the commands are transmit-
ted.
3.5 COMMAND CODES
Each multiline command is given a unique code that that is
transmitted over the bus as 7 bit ASCII data. This section
briefly explains the code groups, which are summarized in
Figure 3-3.
hmmand
GIL
SDC
GET
LLO
DCL
SPE
SPD
LAG
TAG
UNL
UNT
1
Hex Value
01
04
08
11
14
18
19
20.3F
40-5F
3F
5F
3.6 COMMAND SEQUENCES
Addressed Command Group (ACG)-Addressed commands
. .--_. . . . . . _I.~
Decimal Value
1
4
8
17
20
24
25
32-63
64-95
63
95
an* co*esp0n*1ng ASCII codes are listed in cohxnns WA,
and O(B).
Universal Command Group (UCG)--Universal commands
and values are listed in columns l(A) and l(B).
Listen Address Group (LAG)-Columns 2(A) through 3(B)
list codes for commands in this address group. For example, if
the primary address of the instrument is 27, the LAG byte will
be an ASCII left bracket.
Talk Address Group (TAG)-TAG primary address values
and corresponding ASCII characters are listed in columns
4(A) through 5(B).
The preceding address groups are combined together to form
the Primary Command Group (KG). The bus also has
another group of commands, called the Secondary Command
Group (SCG). These are listed in Figure 3-3 for informational
The proper command sequence must be sent to the instru-
ment before it will respond as intended. Universal com-
mands, such as LLO and DCL, require only that ATN be set
low when sending the command. Other commands require
that the instrument be properly addressed to listen first. This
section briefy describes the bus sequence for several types of
commands.
3.6.1 Addressed Command Sequence
Before a device will respond to one of these commands, it
must receive a LAG command derived from its primary ad-
dress. Table 3-3 shows a typical sequence for the SDC com-
mand: the example assumes that a primary address of 27 is
being used.
3-5
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