Operational Control; External Control Subsystem; Controi Console Devices - Xerox 550 Reference Manual

5. OPERATIONAL CONTROL
EXTERNAL CONTROL SUBSYSTEM
The External Control Subsystem (ECS)isa group of elements
used in this computer system that provide operational and
diagnostic interfaces to control and maintain system hard-
ware and software.
CENTRALIZED SYSTEM CONTROL
In many other computer systems
II
software-level
II
operator
interactions are transacted through an operator's teletype-
writer console whi Ie hardware level interactions are per-
formed through a fixed panel of lamps and switches. In
contrast, this Xerox computer system consolidates these in-
teractions and controls into a console telecommunications
device, designated as the System Control Console (SCC).
Through the SCC, the operator has a single control point
for all normal system control activities.
A Remote Diagnostic Interface (RDI) permits the local
System Control Consol e to be augmented wi th a Remote
Console that may have the same degree of system con-
trol. (Usage of the RDI and Remote Console as a Remote
Assist feature is described below, under
II
Remote Console".)
A System Control Panel (SCP) contains indicators and basic
controls that the operator may use during system startup or
to establ ish connections with the remote location.
CONTROL CONSOLE DEVICES
The ECS provides an interface for two local (primary and
alternate) communications consoles and a data set inter-
face for remote diagnostic connection. Each communi-
cations console must have an EIA RS232 voltage interface
and format characters in even parity ASCII code with con-
trol protocols of a Model 4691 KSR 35 Keyboard/Printer.
Allowed communications rates are 10 and 30 characters per
second.
PRIMARY CONSOLE
The primary console always has the functional capability of
the System Control Console to communicate with software
through I/O subchannel address X'Ol'. The communications
rate of the primary console is either 120 characters per
second or the same as the alternate and remote consoles
depending on the setting of the FSELA switch on the Con-
figuration Control Panel (see Chapter 6). If the REMOTE
CHANNEL switch on the System Control Panel is in the
SCC position (implying a remote diagnostic connection),
the remote channel frequency is automatically enforced on
the primary console.
REMOTE CHANNEL
The alternate and remote consoles share the same data paths.
Both consoles receive the same output; either one of the
consoles is selected for input by the ALTSEL switch on the
Configuration Control Panel. The communications rates
of 10 or 30 characters per second are selected for both con-
soles by the FSELBO and FSELB 1 switches on the Configu-
ration Control Panel. Both consoles may function either
strictly as I/O devices or as parallel System Control Con-
soles selected by the REMOTE CHANNEL switch on the
System Control Panel. Description of communications rate
selection is found in Chapter 6.
ALTERNATE CONSOLE
The alternate console normally functions as an output de-
vice residing at I/O subchannel address X'OB'. This con-
sole can create an edited system log, while the operator's
c'onsole functions at a higher communications rate. (RE-
MOTE CHANNEL and ALTSEL switches are both OFF.)
If the primary console fails, the alternate console may
function as the System Control Console. In this case, the
remote console connection is only inhibited by the op-
erator at the data set. (REMOTE CHANNEL switch in
SCC position; ALTSEL switch in ON position.)
Before the remote device can gain access to the Remote
Diagnostic Interface (RDI), the operator must manually in-
tervene to establish the connection at the data set and the
System Control Panel. The data set (Bell 103A or equiva-
lent) connection is inhibited while the REMOTE CHANNEL
switch is in the OFF position.
The remote console may run on-line diagnostics while the
rest of the system performs non-maintenance work. In this
case, the remote console preempts I/O subchannel X'OB'
and the alternate (local) console creates a log of the on-
line mainentance if not turned off.
The remote device
does not have access to the SCC hardware controls, but
may enter software-level control information through the
I/O system (REMOTE CHANNEL switch in I/o position,
ALTSEL switch in OFF position).
If the entire system is under the discretionary control of re-
mote maintenance personnel, the operator may connect the
remote console to the RDI as the System Control Console.
The remote console is then connected logically in parallel,
and assumes all the functional capability of the primary con-
sole, and shares I/O subchannel X'Oll. (Note that con-
ventions must be established to ensure that the primary and
remote consoles do not generate overlapping input.) The
remote console communications rate is automatically im-
posed on the primary console and the operator may have to
Operational Control 135