SERIES
9900
9000
SERIES
GAUSSMETERS
SECTION VIII continued
Series-9900 Theory o f Operation
The +5 V digital power supply is converted to ±10 Vdc for the display module
and to 90 Vac/400 Hz for the display backlight. Interconnection to both the
display module and the pushbutton switches is made through multiple-
contact connectors on the front end of the
processor card.
A subset of the processor's address and control buses, and the entire data
bus, are brought out to the backplane through bus interface components.
These are used to access the
peripheral control card.
VIII-D PERIPHERAL CONTROL CARD
The
peripheral control card,
contains all the components necessary to access
the three
probe-interface modules
as well as the communications ports. The
PCC acts as an extension of the
processor card.
The interface to the
probe-interface modules
is completely isolated using
high-speed optocouplers. This reduces noise in the sensitive analog
sections of the modules by separating the high-noise switching environment
of the digital section from the low-noise steady state conditions in the analog
sections of the module. To control the various functions on the probe
modules, a bit-mapped scheme is used. Via the
peripheral control card,
the
processor can access 64 individual control lines per module. Additionally,
each probe module slot has a set of private backplane lines that control the
transfer of serial data from the module's A/D converter. The serial data stream
is converted to 16-bit wide parallel data on the PCC before being transferred
to the processor. Each conversion generates a private interrupt to the
processor card, one for each slot.
The RS-232 communications port is controlled by a programmable
asynchronous communications element. This component generates the
proper baud rate timing and line characteristics for the full duplex operation of
the port. The serial data and control line logic levels are converted to the
appropriate RS-232 levels by several line translation devices. The lines
terminate at the 25-pin "D" connector via the backplane. The communications
controller can be programmed to generate a private interrupt to the processor
card for various conditions of the port.
The IEEE-488 (GPIB) bus is controlled by a programmable GPIB interface
controller. The controller handles the many activity states of the IEEE-488
protocol. The data and control lines from the GPIB controller interface to the
bus through several GPIB line transceivers. These lines terminate at the 24-
pin IEEE-488 connector via the backplane. The controller can be
programmed to generate a private interrupt to the
processor card
for various
conditions on the bus.
VIII-E PROBE INTERFACE MODULE
The
probe interface module
assembly converts the low-level analog signals
from the probe to high-accuracy digital information that can be manipulated by
the processor section of the gaussmeter.
The processor-to-module interface is completely isolated using optocouplers
to minimize noise. The logic section of the module decodes the bit-mapped
information from the processor to produce individual control and status lines.
The control lines are used to select amplifier range settings, magnitude and
type of Hall device control current, the A/D input source, suppression (dc
zeroing) network range settings, the magnitude and phase of suppression
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