APOLLO Command Module
The APOLLO Command Module (ACM) performs the digital logic functions
associated with:
- keeping track of time (counting clock pulses),
- opening the APD gate in anticipation of photon arrival,
- controlling the duration of the APD gate
- firing the laser in synchrony with the rotating mirror,
- telling the 50 MHz stage when to send a STOP pulse to the TDC,
- sending a time request to the GPS clock once per second,
- controlling entry into "stare" mode, allowing the APD to
sense stars
- blocking the laser when safety demands,
- and calibrating the TDC with pulses separated by precise multiples
of 20.00 ns.
The functions of the ACM have been implemented as a custom CAMAC module
based on Altera MAX 7000AE programmable logic devices (PLDs). Specifically,
an EPM7256AE chip is used to provide the CAMAC dataway interface and
house the module's command set. An EPM7512AE chip is clocked at 50 MHz,
and produces the state logic that drives the APDs, the laser, and
selects STOP pulses for the TDC.
The PLDs residing in the ACM can be re-programmed in situ, allowing
arbitrary modifications to the logic provided the pinouts and external
hardware are the same. This means that new modes of operation not yet anticipated can be accommodated in the future.
Pictures of the ACM
ACM Module
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Close-up view
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ACM Waveform
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Many thanks to Tim van Wechel and Allan Myers (and CENPA) for their fantastic
job in producing the ACM.
APOLLO Apparatus Page
APOLLO Main Page