Tektronix DM 5010, Инструкция по эксплуатации

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Theory of Operation— DM 5010
processor addressing, an Address Bus Buffer stage is
necessary to increase current drive capability.
The Data Bus Buffer serves much the same purpose but
is bidirectional; i.e., it buffers data signals both from and to
the microprocessor.
The ROM circuitry contains the instruments operational
firmware that tells the Microprocessor how to control and
perform instrument functions. Many functions the processor
performs require some way to temporarily store data and
read it back later. The RAM serves this purpose.
A special CMOS RAM is used to store “calibration
constants" for the instrument. During adjustment of the in­
strument, specific signals are applied to its inputs and the
microprocessor is “told" what the readings it is receiving
from
the D/A converter represent. Constants are derived
from this data and are stored in the CMOS RAM. This mem­
ory may only be changed during the adjustment procedure.
The Battery circuit connected to the CMOS
RAM ensures
that these constants are maintained when instrument power
is turned off.
The Front-Panel Control block provides the circuitry nec­
essary for the microprocessor to read information from the
user-selectable Front-Panel Switches as well as the ability
to present measurement data and some status information
back to the user via the Front-Panel Display. The Front-
Panel Drive circuitry provides the current drive necessary to
illuminate the various devices of the Front-Panel Display.
The GPIB (General Purpose Interface Bus) circuitry en­
ables the DM 5010 to communicate with other GPIB-com-
patible instruments. By using an external controller, other
GPIB instruments may receive measurement information
from the DM5010 or may send measurement related
instructions to it. This allows the DM 5010 to change mea­
surement modes and send the measurement results to a
desired instrument without operator intervention.
When a GPIB controller addresses an instrument on the
GPIB, the microprocessor looks at the DM 5010’ s Switches
block to see if it is supposed to respond. These Switches
may be set by the user to define which GPIB address the
DM 5010 will recognize.
One of the Switches, when set, stops all normal oper­
ation of the DM 5010. This is its signature analysis mode,
and signature analysis troubleshooting may be performed
on the instrument. By disconnecting the Data Bus Buffer
from the Microprocessor and connecting the NOP (no-oper­
ation) Buffer in its place, a more rudimentary form of
troubleshooting may be performed.
DETAILED CIRCUIT DESCRIPTION
The following description provides detailed information
about the circuitry of the DM 5010. The diamond numbers)
preceding the individual descriptions indicate the specific
diagram(s) being explained by that description.
INPUT SWITCH < 1>
The Input Switch determines whether the analog signal
applied to the DM 5010's front-panel inputs or the signal
from the analog inputs at its rear interface connector is mea­
sured.
Depending on the range of the measurement being
made, the input is attenuated by an appropriate factor to
prescale the signal and protect the various input circuits
from overvoltage conditions.
With no current through relay K1631, the front-panel in­
puts HIGH, LOW, and GUARD are selected for measure­
ment. Guard switch S1731 allows the user to select the
guard configuration most suited for his measurement re­
quirements. Resistor R1626 provides a known impedance
of 1 MΩ between the GUARD and LOW inputs with the
Guard switch open. Refer to the Operating Instructions in
Section 2 for specifics concerning use of the GUARD input.
The internal Guard is connected to the rear LO when using
the rear interface inputs.
With the low (-27 V) applied to K1631-4, indicating that
measurements should be taken from the rear interface con­
nector, current to activate the relay flows through both
R1613 and CR1621. Once activated, the current path
through R1S31 is opened and only the smaller current nec­
essary to keep the relay activated flows in the relay via
CR1621 and R1615.
4-4
ADD JAN 1982