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Principles of Operation
MAU POWER CONTROL CIRCUIT.
The MAU power control circuit provides three functions:
I2-Volt Switch
The Z-80B MPU can turn the 12V to the AUI on or off.
12-Volt Current Protect
If
the current to the AUI goes above 1. 2A, the power control circuit switches the + 12V off, thus
protecting the LANIC and the system from shorts in the ThinMAU. The Z- 80B will detect the fault
and attempt to restart MAU power.
If
the attempt fails, the Z- 80B notifies the host system of the
fault.
12-Volt Sense
The Z-80B can determine if power to the AUI is on or off. However, it is not able to accurately
measure the exact voltage being supplied. The IEEE 802.3 standard requires VP
(+
12V) to be greater
than 11. 28 volts.
It
is possible that the + 12-volt power supply may be adjusted low enough such that
less than 11. 28 volts is present at the LANIC edge under load. If faulty ThinMAU operation is
suspected, and ThinMAU replacement has not corrected the problem, the VP voltage should be
checked. The VP voltage can be checked by connecting an accurate voltmeter between the + 12V and
GND test points on the LANIC.
If
the voltage under load is found to be less than 11. 28V, the system
+ 12V power supply must be checked and adjusted to the upper end of the allowable range. If the
power supply is already set at the upper end of its range, the LANIC may need to be replaced.
Consult the appropriate CE
Handbook
for details.
LED's.
The LANIC uses 15 LED's to: monitor activities on the card and the LAN network. The locations of the
LED's are shown in Section 2, figure 2-1; the labels and functions of the LED's are shown in figure 3-3.
The seven LED's labeled A through G monitor activity on the AUI interface. The eight LED's labeled
H
through Nand
*
monitor LANIC MPU activity, A great deal of information about the state of the
network and the LANIC and system software can be gained by studying the LED's. They are provided as
an aid in problem detection and resolution.
Each of the 15 LED's is labeled with two different labels. The single alphabetic labels are helpful for
quick reference to the LED's; the two-letter mnemonics are intended to remind users of the function
being indicated by the LED.
11/85
3-12
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