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MAU Power Control Circuit
The MA V power control circuit provides three functions:
1.
12-Volt Switch: The Z-80B MPU can turn the 12V to the AUI on or off
2.
12-Volt Current Protect: If the current to the AVI goes above 1.2A, the
power control circuit switches the +12V off, thus protecting the LANIC and
the system from shorts in the AUI cable or MAV. 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.
3. 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 GNO 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 C E H andhook for details.
LEOs
The LANIC uses 15 LEOs to monitor activities on the card and the LAN
network. The locations of the LEOs are shown in Chapter 2, Figure
2-1;
the
labels and functions of the LEOs are shown in Figure 3-3.
The seven LEDs labeled A through G monitor activity on the A UI interface.
The eight LEDs 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 LEDs. They are provided as an
aid in problem detection and resolution.
Each of the 15 LEOs is labeled with two different labels. The single alphabetic
labels are helpful for quick reference to the LEDs; the two-letter mnemonics are
intended to remind users of the function being indicated by the LED.
Principles of Operation
3-15
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