Digital Equipment LA400, Руководство по обслуживанию

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Maintenance Manual Electronic Hardware Overview
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3.1.3.1 D.O.E. Block Features
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RESET and PREFAULT
This block handles some important signals indispensable for the correct intialization of
the microprocessor and power drivers during the power-on and power-off transitions
phases.
There is a Voltage Supervisor TL7705A that monitorizes the voltages during the
transition phases and a Schmitt Trigger that rigenerates the signal edges for the logic
HCMOS compatibility.
This circuit is supplied with the analogic "or" of the two vo5 and +38.
In this way it is ready if only one voltage is present.
It generates the CPU Reset when the logic voltage r4.75V.
It also generates the PREFAULT signal to handles the printer status in the NVM.
In the next two figures are shown the schematics and the typical vaweforms of this
circuit.
Typical timing:
with +38 V = +10V and with +5V = +4.4V the signal are as point A.
TD-TB > 30 msec.
TF-TE > 2 msec.
Figure 3.5 Reset and Prefault Circuit
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LA400 Multiprinter 3. 11 ER-LA400-SV