Hp-Ib Status Indicators; Bus Device Modes; System-Controller Mode - HP 8753E Programming And Command Reference Manual

When the analyzer is to other instruments over the HP-IB,
the HP-IB status indicators illuminate to display the current status
of the analyzer. The HP-II3 status indicators are located in the
instrument-state function block on the front panel of the network
analyzer.
R = Remote Operation
L = Listen mode
T = 'Iblkmode
S = Service request (SRQ) asserted by the analyzer

Bus Device Modes

The analyzer uses a single-bus architecture. The single bus allows both
the analyzer and the host controller to have complete access to the
peripherals in the system.
Three different controller modes are possible in an HPIB system:

system-controller mode

n
talker/listener mode
n
pass-control mode
n
HP-IB Programmi ng and Command Reference Guide