Adex ISAIX16 Manual do utilizador - Página 6
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THEORY OF OPERATION
The Bus Isolation Extender provides bus signals and power
isolation between the system motherboard and the add-on board
on the extender. The signals are isolated using state of art analog
switches that allows bi-directional signal flow. When the analog
switches are turned off, the bus signals at the extender side are
isolated from the system bus. When the analog switches are
turned on, the bus signals are connected. The analog switch
provides no signal "buffering". That means, the bus signals are
not reconditioned at TTL levels, nor are they redriven by any
active amplifier. Any AC/DC signal loading on the add-on board
will have a direct effect on the signal lines on the system
motherboard. The analog switch introduces only less than 250
picoseconds delay to the signals. Such minimal delay makes the
analog switch suitable for very fast bus operation.
The power isolation is implemented using MOSFETs. The
MOSFETs are biased to allow slow ramping up of current through
the Bus Isolation Extender to the add-on boards without causing
a power surge or glitch to the system power. When the voltage
on the +5V line on the add-on board reaches above 4.5 volts, the
logic on the extender will turn on the analog switches to connect
the bus signals. When the Bus Isolation Extender is switched off,
the logic on the extender board will disconnect the bus signals
immediately, and shut down the power slowly.
In addition, a 16ms reset pulse is generated to the add-on board
on top of the extender, whenever the extender is switched on. If
the system issues a reset pulse while the bus is connected, the
extender will pass that reset pulse to the add-on board without
disconnection or reconnection.
An on-board red status LED will blink about twice a second,
when the power and the signals are completely connected
between the add-on board and the system bus. The red LED will
stay off, if the Bus Isolation Extender is turned off or if the +5 and
+12 volts do not reach operating voltages within 16ms after
power up.
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Adex Electronics
ISAIX16 User's Manual
During operation, if a short circuit condition is developed between
+5 and +12V to ground, the logic will shut off the power and the
red LED. The speaker will buzz in a continuous tone to alert the
operator. User needs to switch the extender off, to reset the short
circuit logic.
The add-on boards should be inserted or removed from the
extender only when the extender is switched off and the red LED
is not blinking and the speaker is not buzzing. Serious damages
to the system, extender and the add-on board could happen
if the add-on board is inserted or removed when the bus is
still connected.
LOCAL and EXTERNAL CONTROL
The Bus Isolation Extender has an unique external control
feature. This feature is very useful in production environment and
it can be easily implemented in many ways. It allows external
toggle switch or TTL logic inputs to control the operation of the
extender. When used with proper software, this feature helps to
automate the test process without requiring manual switching by
the operator. This external control feature is accessible through
the W7 header located by the on-board toggle switch. The header
is keyed for ribbon type of connector interface. The 2X5 header
has the pins defined as on page 7 under W7 Pin headers.
ON-BOARD TOGGLE SWITCH OPERATION
This is the default operation mode as configured by the factory.
This configuration allows single toggle switch operation without
any external connection. A jumper is installed between pin 1 and
pin 3 of the W7 header. It requires an operator to manually
toggle the switch up for bus connection and toggle it down for bus
isolation. When the switch is toggled up, both the power and the
signals are connected by the on-board logic.
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