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H Through Nand .. LEDs
When the LANIC has been reset either by power-up of the system or by the
operating software. all eight of the MPU activity indicators (LEOs H through N
and *) will be on continuously. This indicates that the MPU is not executing.
Additionally. the VP LED will be off. which indicates that the MAU is not
powered. The other AUI activity indicator LEOs will all be off.
After the LANIC has successfully passed self test. and the pass code pattern has
been displayed as required. the
*
LED will be off. and the other seven MPU
activity indicator LEOs will now indicate the MPU activity. The
*
LED being
off indicates that the H-N LEOs are to be interpreted as individual activity
indicators according to their two-letter mnemonics. (See the following
paragraphs.)
TX, RX, MN, DL,
RO,
Q,
and IT LEOs
When self test passes. the SPU is interrupted and notified of the event. Between
the time that this interrupt is given and the time when the SPU begins to access
the LANIC. the RO and Q LEDs will be lit. This indicates that the LANIC is
executing ROM code and is quiescent. while waiting for the SPU to take control.
In addition. the VP LED will be lit. indicating that the MAU is powered. Any
activity on the network coaxial cable will be indicated by the state of the CL
and CR LED pairs. The LANIC will never transmit in this state. and therefore.
the DO LED pair will remain inactive.
When the SPU prepares the LANIC for operation. it first must download the
operating firmware from system memory to the LANIC. When this process
begins. the DL LED turns on. and the
Q
and IT LEOs will go off. After each
download command. the
Q
LED lights for a few milliseconds.
At least seven
download commands occur, but they may not be separately distinguishable.
However. the pattern that occurs on one working system will occur on all other
working systems. so if suspicious. compare the download pattern on the suspected
system with a system that works.
After the download is complete. the SPU will instruct the MPU to begin to
execute the downloaded firmware. When this occurs. the RO and DL LEOs will
go off. The
Q
and IT LEOs will turn on.
A short time later the SPU will instruct the LANIC to set its individual address.
When this occurs. the LANIC performs a duplicate address check. which is
accomplished by transmitting 10 frames to the network with a 500 millisecond
separation between frames. The TX and the DO E LED will both come on for
each of the 10 frames. In addition. the CR E LED will indicate that the frames
were sent to the coaxial cable and caused the carrier to come on. If collisions
are encountered, the frames will be retried up to 15 times each, with resultant
activity indicated by the CL LEOs. The RX LED will not light during the
duplicate address check due to our own transmission. even though the duplicate
address check frame is addressed to the transmitting LANIC. If the RX LED
lights during duplicate address checking. it is due either to a duplicate station
Principles of Operation
3-20
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