42
CHAPTER 5:
Computer Interface Operation
Model 648 Electromagnet Power Supply
5.2.1 Changing IEEE-
488 Interface
Parameters
The IEEE-488 address must be set from the front panel before communication with
the instrument can be established.
Menu Navigation:
Interface
Q
Enabled
Q
IEEE-488
Interface
Q
IEEE-488 Address
Q
(1 to 31)
Default: IEEE-488.
5.2.2 Remote/Local
Operation
Normal operations from the keypad are referred to as local operations. The
Model 648 can also be configured for remote operations via the IEEE-488 interface or
the
Remote/Local
key. The
Remote/Local
key will toggle between remote and local
operation. During remote operations, the remote annunciator LED will be illumi-
nated, and operations from the keypad will be disabled.
5.2.3 IEEE-488
Command Structure
The Model 648 supports several command types. These commands are divided into
four groups.
1. Bus control (section 5.2.3.1)
a. Universal
D
Uniline
D
Multiline
b. Addressed Bus Control
2. Common (section 5.2.3.2)
3. Device specific (section 5.2.3.3)
4. Message strings (section 5.2.3.4)
5.2.3.1 Bus Control Commands
A bus control command can either be a universal or an addressed bus control. A uni-
versal command addresses all devices on the bus. Universal commands include uni-
line and multiline commands. A uniline command (message) asserts only a single
signal line. The Model 648 recognizes two of these messages from the Bus Controller:
Remote (REN) and Interface Clear (IFC). The Model 648 sends one uniline command:
Service Request (SRQ).
D
REN (Remote): puts the Model 648 into remote mode
D
IFC (Interface Clear): stops current operation on the bus
D
SRQ (Service Request): tells the bus controller that the Model 648 needs interface
service
A multiline command asserts a group of signal lines. All devices equipped to imple-
ment such commands do so simultaneously upon command transmission. These
commands transmit with the Attention (ATN) line asserted low. The Model 648 recog-
nizes two multiline commands:
D
LLO (Local Lockout): prevents the use of instrument front panel controls
D
DCL (Device Clear): clears Model 648 interface activity and puts it into a bus idle
state
Finally, addressed bus control commands are multiline commands that must include
the Model 648 listen address before the instrument responds. Only the addressed
device responds to these commands. The Model 648 recognizes three of the
addressed bus control commands:
D
SDC (Selective Device Clear): the SDC command performs essentially the same
function as the DCL command, except that only the addressed device responds
D
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.
