Agilent Technologies 54502A Manuale di Servizio Scaricare il pdf (Pagina 90)

Theory of

Operation

The HP 1650B/51B Logic Analyzer is an 80/32 channel state and timing logic

analyzer. The human interface is a front-panel keypad and knob for instrument

control and 9" (diagonal) white phosphor CRT for information display. Available

on the rear panel are RS-232-C and HP-IB ports for communication to a printer or

from a controller. Also on the rear panel are two BNCs for input or output of an

external trigger.

The System Assembly Board is built around the 68000 microprocessor and

powerful data acquisition ICs that probe, shape, store, and analyze data from a

target system. An acquisition interface to the 68000 makes the acquisition system

fully compatible with the architecture of the 68000 microprocessor. The System

Assembly contains the necessary circuitry to interface the keypad, CRT monitor,

disk drive, RS-232-C and HP-IB ports.

Figure 6-1 is a simplified block diagram of the instrument. The hardware of the

HP 1650B/51B consists of four main assemblies. Also shown are rear panel

connectors. This manual supports troubleshooting to assembly level. Theory of

operation for the System Assembly is included for information only and is not

intended for troubleshooting purposes.

Data Acquisition The data acquisition of the System Assembly consists of the data acquisition pods,

acquisition ICs, and the interface to the 68000. The interface to the target system

is through any of the data acquisition pods. There are five pods available on the

HP 1650B (80 channels) and two pods available on the HP 1651B (32 channels).

Each pod contains 16 input data probes and one external clock input for state

mode measurements. The data probes can be used for state or timing

measurements.

Each pod consists of a probe tip assembly and a 4.5 foot woven cable. A probe tip

assembly includes 17 twelve-inch probes and a common ground return. This is

connected to one end of the cable. The other end of the woven cable terminates at

the rear panel of the logic analyzer. The woven cable consists of 17 nichrome

signal lines, 34 signal return lines and 2 power supply lines. All are woven together

with polyarmid yarn.

Each probe input has an input impedance of 100k ohms in parallel with

approximately 8 pF. The probes can be grounded in two ways: with a common

pod ground for state measurements, or a probe tip ground for higher frequency

measurements.

The input signals are attenuated by a factor of 10 in the passive probe. The signals

are applied to a comparator where they are compared against a voltage threshold

to determine if the voltage level is above or below the threshold level. The

comparator then shapes the single-ended signal and outputs it at an ECL level to

the acquisition IC. The input data is then stored at the acquisition IC.

Arming Control The two BNCs on the rear panel are used for arming control of the logic analyzer

acquisition ICs. An arm signal may be output from the ICs to the rear panel

EXTERNAL TRIGGER OUT (J10), or input to the ICs from EXTERNAL

TRIGGER IN (J9).

HP 1650B/1651B Service

Service Manual 6-3

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Agilent Technologies 54502A Manuale di Servizio Pagina 90

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