Lakeshore 340 User Manual page 100

9.1.2.1 Bus Control Commands
A Universal Command is a command that addresses all devices on the bus. Universal Commands include
Uniline and Multiline Commands. A Uniline Command (Message) is a command which results in a single
signal line being asserted. The Model 340 recognizes two of these messages from the BUS CONTROLLER:
Remote (REN) and Interface Clear (IFC). The Model 340 sends one Uniline Command (SRQ).
REN (Remote) – Puts the Model 340 into a remote mode.
IFC (Interface Clear) – Stops current operation on the bus.
SRQ (Service Request) – Tells the bus controller that the Model 340 needs interface service.
A Multiline Command involves a group of signal lines. All devices equipped to implement such commands do
so simultaneously when the command is transmitted. These commands are transmitted with the Attention
(ATN) line asserted low. There are two Multiline commands recognized by the Model 340:
LLO (Local Lockout) – LLO is sent to instruments to lock out (prevent the use of) their front panel controls.
DCL (Device Clear) – DCL is used to clear Model 340 interface activity and put it into a bus idle state.
Finally, Addressed Bus Control Commands are Multiline commands that must include the Model 340 listen
address before they respond to the command in question. Note that only the addressed device responds to
these commands. The Model 340 recognizes three of the Addressed Bus Control Commands:
SDC (Selective Device Clear) – The SDC command performs essentially the same function as the DCL
command except that only the addressed device responds.
GTL (Go To Local) – The GTL command is used to remove instruments from the remote mode. With some
instruments, GTL also unlocks front panel controls if they were previously locked out with the LLO command.
SPE (Serial Poll Enable) and SPD (Serial Poll Disable) – Serial polling is used to obtain the Service
Request (SRQ) Status Register. This status register contains important operational information from the unit
requesting service. The SPD command ends the polling sequence.
9.1.2.2 Common Commands
Common Commands are addressed commands intended to make some commonalty between instruments on
the bus. Instruments that comply with the IEEE-488.2-1987 standard share these commands and their format.
Common commands begin with an asterisk (Q). They are usually related to "bus" and "instrument" status and
identification. Common query commands end with a question mark (?). A list of Model 340 common
commands is provided in Paragraph 9.3.
9.1.2.3 Interface and Device Specific Commands
Device Specific Commands are addressed commands. The Model 340 supports a variety of Device Specific
commands to allow the user to program the controller remotely from a digital computer and to transfer
measurements to the computer. Most of the Device Specific commands have a function that can also be
performed from the front panel. This section discusses Common and Device Specific commands. The Device
specific commands are further broken down into Interface, Display, Channel, Control Process and Curve
commands for user convenience. A table of every command of each type is presented and is immediately
followed by individual discussions of each command. These discussions are handled in the format described
below. A list of Model 340 commands is provided in Paragraph 9.3.
9-2
Lake Shore Model 340 Temperature Controller User's Manual
Remote Operation