Star Tech Journal

S~R-TECH __ _ _ __ _ _ _ _ _ 7
The manner of connecting the logic pulser into the circuit
under test is quite simple. The logic pulser has two power
leads that are connected to the Vee and ground points in the
circuit. Any DC voltage from +3 to +18 volts, with a current
capability of 35 mA, will cause the logic pulser to operate
properly. With the power leads connected, merely touch the
probe of the logic pulser to the desired point in the circuit and
generate a signal by tapping and pressing the pulse button as
previously described.
HEWLETT PACKARD
546 LOGIC PULSER
PULSE BUTTON
CODE
OUTPUT
•
SINGLE PULSE
·-
CONTINUOUS 100 Hz PULSE STREAM
100-PULSE BURST
. . . . -
10 Hz PULSE STREAM
10-PULSE BURST
1 Hz PULSE STREAM
•
ONE PRESS OF BUTTON
-
PRESS AND LATCH
FIGURE 8
The Hewlett-Packard 546 Logic Pulser automatically senses
the signal level at the test point and will drive a high level low
or a low level high to produce the pulse. It is overload
protected and is capable of delivering a 0.5 microsecond
pulse of approximately 650 milliamps. With a low output
impedance of approximately 2 ohms, the circuit can drive a
TTL line for any circuit condition except a direct short that is
less than two inches from the pulser probe. A short to ground
or Vee less than two inches from the probe presents a low
enough impedance to load down the probe'soutput. The logic
pulser eliminates the need to unsolder integrated circuit pins
or cut the foil on a printed circuito inject signals. Together
with the logic probe, it provides a valuable tool in trouble-
shooting integrated circuit systems.
Figure 9 shows a condition where the output of ICA is shorted
to ground. A static measurement of the circuit with the logic
probe alone might not indicate this fault, since it could very
well be a situation where that point in the circuit is normally at
a logic zero but must momentarily go high in response to a
short pulse. By connecting the logic pulser and the logic
probe to the same point, you would notice that the logic
pulser would be unable to drive the output of ICA above
ground and no pulse would be observed. The logic pulser is
designed so that it can drive a gate that is in either the 1 or the
zero state, but it is unable to drive a ground or a short to Vee
that is physically close to the probe.
LOGIC
PROBE
FAULT
FIGURE 9