ClflCUIT
DESCRIPTIONS
3-9
3.3.4
DIGITAL ASIC (D-ASIC) cicultry
-
Introduction
The Digital Application Specific Integrated Circuit (or
D-ASIC)
D1203
forms the core of the digital
circuitry of the ScopeMeter ail located on the digital A1 PCB.
Many functions are incorporated in this complex CMOS Integrated circuit (see
figure 3.^ on the next
page);
-
Timebase
•
Trigger
•
Acquisition Corttrol Logic
•
Acquisition RAM
-
Min/max
-
Display control
-
Decodmg and synchronization
DIg Ital-to-analog converters ( DAOs
)
-
Detailed circuit description:
See figure 3.4 and circuit diagram At (figure 10.2).
The following gives a short description of the separate
parts
of the
D-ASIC, which perform the
functions mentioned above:
Tlmebase
The D-ASIC contains a crystal oscillator, which uses the 25 MHz crystal G1201. An internal
programmable divider generates timebase sign^ TRACK with a frequency from 0.8333 Hz up to 25
MHz (see section 3.4.5). This TRACK signal is used to sample the ScopeMeter input
signals.
Trigg&r
The
trigger
module in the D-ASIC takes
care
of
all trigger related functions:
•
pre triggering
• post triggering
•
event counting: the time interval corresponding to the trigger delay is Increased by a
programmed number of "evenlB" (trigger level crossings ofihe
external trigger
signal), which must occur before triggering.
•
n-cycle mcxje: trigger level crossings of the input signal are
counted,
and
triggering
occurs
every n'*' crossing
(2
< n < 255). The n-cyde mode can be used as a digilal
trigger hold-off.
In the real-time sampling mode (<
1
ps^dlv), the D-ASIC determines the trigger moment with digital
comparators. In the quasi -random sampling mode,
the
A-ASIC
determines the trigger moment with
analog comparators.
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