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Lake Shore Model 480 Fluxmeter User’s Manual
Computer Interface Operation 6-3
Bus Control Commands (Continued)
Finally, Addressed Bus Control Commands are Multiline commands that must include the
Model 480 listen address before the instrument responds. Only the addressed device responds to
these commands. The Model 480 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 accesses 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.
6.1.2.2 Common Commands
Common Commands are addressed commands which create commonalty between instruments on
the bus. All instruments that comply with the IEEE-488 1987 standard share these commands and
their format. Common commands all begin with an asterisk. They generally relate to “bus” and
“instrument” status and identification. Common query commands end with a question mark (?).
Refer to Paragraph 6.3 for a list of all Model 480 common commands.
6.1.2.3 Interface and Device Specific Commands
Device Specific Commands are addressed commands. The Model 480 supports a variety of Device
Specific commands to program instruments remotely from a digital computer and to transfer
measurements to the computer. Most Device Specific Commands perform functions also performed
from the front panel. This section discusses Common and Device Specific commands. Device
Specific Commands consist of Interface, Display, Channel, and Control Process commands. Refer
to Paragraph 6.3 for a list of all Model 480 interface and device specific commands.
6.1.3 Status Registers
There are two status registers: the Status Byte Register described in Paragraph 6.1.3.1, and the
Standard Event Status Register in Paragraph 6.1.3.2.
6.1.3.1 Status Byte Register and Service Request Enable Register
The Status Byte Register consists of one data byte containing seven bits of information about
Model 480 status.
STATUS BYTE REGISTER FORMAT
Bit – 7 6 5 4 3 2 1 0
Weighting – 128 64 32 16 8 4 2 1
Bit Name –
Not Used
SRQ ESB OVI AAF ALM AAC FDR
If the Service Request is enabled, setting any of these bits causes the Model 480 to pull the SRQ
management low to signal the BUS CONTROLLER. These bits reset to zero upon a serial poll of
the Status Byte Register. Inhibit or enable these reports by turning their corresponding bits off or on
in the Service Request Enable Register.
The
Q
SRE command sets the bits. Setting a bit in the
Service Request Enable Register, enables that function. Refer to the
Q
SRE command.
Service Request (SRQ) Bit (6) – Determines whether the Model 480 reports via the SRQ line. Six
bits determine which status reports to make. If bits 0, 1, 2, 3, 4, and/or 5 are set, then the
corresponding bit in the Status Byte Register is set. The Model 480 produces a service request only
if bit 6 of the Service Request Enable Register is set. If disabled, the BUS CONTROLLER still
examines Status Byte Register status reports by serial poll (SPE), but the Service Request cannot
interrupt the BUS CONTROLLER. The
Q
STB common command reads the Status Byte Register
but will not clear the bits.