DEC 4000 Model 200 Operation Manual page 23

The CPU cover panel has the following components:
Power-Up Mode switch—This three-position rotary switch
determines how the system responds at power-up:
Language Inquiry Mode (in the top position, indicated
by a profile of a face) causes the system to display a
language selection menu at power-up if your console
terminal supports multiple languages. Also, if a default
boot device has not been selected, this mode causes the
system to issue a list of bootable devices and prompts you
to select a device from the list. Once a device is selected,
the system autoboots from that device each time you turn
it on.
Run Mode (in the middle position, indicated by an arrow)
is the normal operating setting.
Loop Back Test Mode (in the bottom position, indicated by
a T in a circle) causes the system to run loopback tests on
the console serial line at power-up. This setting requires
special loopback connectors and is for Digital Customer
Services use only.
Modified modular jack (MMJ)—This console terminal connector
provides the connection for the console terminal.
The light-emitting diode (LED) display shows the testing
sequence during power-up.
Break Enable/Disable switch—When the switch is down (dot
outside the circle), breaks are disabled. When the switch is
up (dot inside the circle), breaks are enabled. When breaks
are enabled, pressing
processor and transfers control to the console program. Using the
console command SET CONTROLP, you can specify the control
character,
on the console terminal halts the
Break
, rather than
Ctrl/P Break
to initiate a break signal.
System Overview 1–13