HP 8508A - Page 54

Operation
aaa
SYSTEMS
Sending the Data Message
The Vector Voltmeter sends Data messages when addressed to talk and has data to output. The output format for
each message is shown in Table 3-2.
Receiving the Remote Message
The Vector Voltmeter switches to remote operation upon receipt of the Remote message. The Remote message
has two parts:
* The Remote Enable bus control line (REN) set true, and
* A Device Listen Address received once (while REN is true).
When the Vector Voltmeter switches to remote, the front panel R annunciator turns on.
Receiving the Local Message
The Local message ‘is the means by which the controller sends the Go To Local (GTL) bus command. If addressed
to listen, the Vector Voltmeter returns to front panel control when it receives the Local message. If the instrument
is in local lockout when the Local message is received, front panel control is returned, but lockout is not cleared.
Unless it receives the Clear Lockout/Local message, the Vector Voltmeter will return to local lockout the next time
it goes to remote. No front panel instrument settings are changed by the transition from remote to local, but the
following parameters are set:
* Trigger State is set to freerun;
* Average Count set to 5;
* Display State on;
When the Vector Voltmeter goes to local mode; the front pane] R annunciator turns off. However, when the Vector
Voltmeter is being addressed (whether in local or remote), its front panel L or T annunciator remains lit.
Receiving the Local Lockout Message
The Local Lockout message is the means by which the controller sends the Local Lockout (LLO) bus command. If
in remote mode, the Vector Voltmeter responds to the Local Lockout message by disabling the front panel [LCL]
key. The local lockout mode prevents loss of system control due to accidentally pressing front panel keys. When in
local lockout mode, the Vector Voltmeter can be returned to local only by the controller (using Local or Clear
Lockout/Local messages) or by setting the LINE switch to OFF and ON.
Receiving the Clear Lockout/Set Local Message
The Clear Lockout/Local message is the means by which the controller sets the Remote Enable (REN) bus control
line false. The Vector Voltmeter returns to local mode (full front panel control) when it receives the Clear Lock- .
out/Set Local message. When the Vector Voltmeter goes to local mode, the front panel R annunciator turns off.
3-30
E1089
ee@Menennanenezene Beeveuanuntenenunzunn@uzan