Global Specialties 3600 - Manual (Page 15)

Users Manual Model 3600
www.globalspecialties.com Page 10
be used). The voltage will increase by turning the knob to right and
decrease by turning the knob to left. When the voltage value passes
the zero, the polarity sign will automatically change. The internal
code-generator doesn’t pass the voltage comparator, so the settings on
threshold voltage aren’t valid when sampling the internal code.
The analyzer has 32 external signal input channels and 2 external
clock channels. The best performance is when the peak-to-peak value
of input voltage is between 500 mVpp and 20 Vpp. The maximum
input voltage the instrument can handle is ±40 V. After accessing the
analyzer, the input signal first passes through the voltage comparison
circuit and is compared with the threshold voltage set by the user. If the
input signals are higher than the threshold voltage, the analyzer shows
the number “1”, otherwise it displays the number “0”. Then the signals
are sampled and saved and displayed on the screen.
Waveforms displayed by this means only reflect the timing logic when
the input signals are higher or lower than the threshold voltage. It
doesn’t reflect the real amplitude of the input signals, and may be far
different from the real waveforms of the input signals. This kind of
waveform displayed by the logic analyzer is usually called a “pseudo
waveform”.
Sampled Signals
In practical operation, the sampled signals appear by groups.
For example, grouped by the data bus or the address bus .The
characteristics of amplitude of a group of signals are the same, so use
the same compare threshold voltage. The amplitude characteristics of a
group of signals are the same, so use the same comparative threshold
voltage. In practical operation there are many kinds of signals with
different amplitudes to be tested, such as TTL, CMOS and ECL. In every
experimental circuit, the amplitude characteristics of signals may be
various. To satisfy these conditions, the instrument is deployed with
six individual adjustable threshold voltages. Four of them are used in
four channel groups which contain 8 signal input channels in each one.
And the other 2 threshold voltages are used in 2 external clock input
channels.
Measured Signals
In practice, the instruments measures signals in groups, for instance
Model 3600 User Manual_B.indd 10 7/2/2010 4:41:44 PM