Digital Asic (D-Asic) Circuitry - Philips SCOPEMETER PM93 Service Manual

CIRCUIT DESCRIPTIONS
3-9
3.3.4 DIGITAL ASIC (D-ASIC) circuitry
- Introduction
The Digital Application Specific Integrated Circuit (or D-ASIC) D1203 forms the core of the digital
circuitry of the ScopeMeter, all located on the digital A 1 PCB.
Many functions are incorporated in this complex CMOS integrated circuit (see figure 3.4 on the next
page):
- Timebase
- Trigger
- Acquisition Control Logic
- Acquisition RAM
- Minimax
- Display control
- Decoding and synchronization
- Digital-to-analog converters (DACs)
- Detailed circuit description:
See figure 3.4 and circuit diagram A 1 (figure 10.2).
The following gives a short description of the separate parts of the D-ASIC, which perform the
functions mentioned above:
Timebase
The D-ASIC contains a crystal oscillator, which uses the 25 MHz crystal G1201. An internal
programmable divider generates timebase signal 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.
Trigger
The trigger module in the D-ASIC takes care of all trigger related functions:
- pre triggering
- post triggering
- event counting:
- n-cycle mode:
the time interval corresponding to the trigger delay is increased by a
programmed number of lIevents ll (trigger level crossings of the external trigger
signal), which must occur before triggering.
trigger level crossings of the input signal are counted, and triggering occurs
every nth crossing (2 < n < 255). The n-cycle mode can be used as a digital
trigger hold-off.
In the real-time sampling mode « 1 /-1s/div), 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.