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2-32
Theory of Operation
The SELF TEST switch latches to allow continuous self-test. Bit 13 in R2 is set while the SELF
TEST switch is latched. The service panel output module code in the loader ROM reads that bit to
see if the SELF TEST switch is latched. If it is, and no loadee can be found to load, self-test is
restarted by writing a 24 hex to Rl following a few seconds delay for stack cooling.
Non-Maskable Interrupt
This interrupt allows an
110
card to reset the processor. The software is informed of this interrupt by
a poll response and bit 14 of R2 set. An
110
interface clear (IFC) is issued to remove the poll
response. Jumpers on the SCM can connect this line to the power supply reset or self-test signals.
Service Panel Switches
Three momentary switches on the service panel cause a poll response and bits in R2 to be set. The
switches are RESET (bit 0), START (bit 12), and MEM DUMP (bit 15). They can be cleared by
writing a 10 hex to Rl.
14.7456 MHz Clock
This clock is generated on the SCM, buffered, and sent to the
110
backplane. It is used by the
110
cards for baud rate generation and for driving state machines.
Service Panel
The service panel, located behind the computer front panel, provides all the information necessary
to diagnose hardware failures to the level of a field-replaceable module. The control logic for the
service panel is on the SCM and consists of a microprocessor and supporting circuits.
The service panel has 4 switches and 27 LEOs. The switches are defined as: RESET, START,
MEM DUMP, and SELF TEST. The LEOs are defined as POWER ON, RUN, SELF TEST, and
there are several fault-indicating LEOs.
Switches
The following paragraphs define the four switches on the service panel.
RESET Switch
When this momentary pushbutton switch is pressed it causes the system to reset via a software
interpretation of an SCM board poll response and status message. All programs running in the
machine are stopped and the RUN LED is turned off. After reset is complete, the system waits for
the START or MEM DUMP switch to be pressed.
START Switch
When the START switch is pressed, the auto-start procedure is initiated. System powerup also
initiates auto-start. The auto-start procedure automatically loads a selected program which starts up
the user's application.
If no auto-start file is found, the system enters an idle state and waits for an external stimulus. If a
system console or operator interface is attached to the computer, the operator or programmer has
control of the system and can bring up the system manually.
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