Martel Electronics 3001 - Manual (Page 46)

An important thing to note about interface messages is that, unlike device-
dependent and common commands, interface messages are not sent literally
(in a direct way). They are converted to parallel signal levels on the bus data
and control lines.
IEEE-488 standards define interface messages which are handled automatically
in most cases.
e) Compound Commands
A compound command is two or more commands placed on a single
command line separated from each other with semicolons. For example,
consider the following two individual commands:
OUT 1 V
OPER
These could be combined into the compound command:
OUT 1 V; OPER
These commands instruct the 3001 to source 1 V DC, and then go into operate
mode.
f) Overlapped Commands
Commands that begin execution but require slightly more time than the normal
communication command/response interval to complete are called overlapped
commands. This is because they can be overlapped by receipt the next
command before they have been completed.
The detailed command descriptions in section 10 show a check mark T beside
Overlapped for overlapped commands.
Use the command *WAI to wait until the overlapped command has completed
execution before executing the next command. For example:
OUT 1 V; *WAI
You can also use the status commands *OPC and *OPC? to detect the
completion of overlapped commands.
g) Sequential Commands
Commands that execute immediately are called sequential commands.
The detailed command descriptions in section 10 show a check mark T beside
Sequential for sequential commands.
The majority of commands are sequential.
h) Commands for RS-232 Only
Several commands are used only for RS?232 serial operation because these
functions must be implemented as IEEE uniline (single control line) bus
management messages per the IEEE Standards. For example, the command
REMOTE could be sent as data over the IEEE-488 interface to place the 3001
into remote operating mode, but it is not because the IEEE Standards call for
the remote function to be sent to the device as the uniline message REN. This
is also true for several other commands and functions, as shown in table 6
below with their RS-232 equivalents.
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