[evla-sw-discuss] total power

[George Peck]

The ALMA requirements for the Total Power Digitizer Board probably are
somewhat different than the requirements for the EVLA.  For ALMA,
samples are taken every 2 ms, and are stored in a FIFO on the Total
Power Digitizer Board.  Once every 48 ms, the FIFO is read out by the
AMBSI (ALMA equivalent of the MIB).  The AMBSI sends the data to the
main computer using a series of CAN messages.  There is an onboard PIC
microprocessor on the board, so that the AMBSI only has to get data on
and off of the board.  The ALMA board uses a 25 MHZ clock, as well as
a 48 ms pulse (provided external to the module) to create a 500 Hz
clock for the circuit.  

It is probable that a similar, but not identical design could be used
for EVLA.  It will depend on how often samples are taken, and how
often they must be sent out over the ethernet.  It probably would be
quite easy and cheap to design a board that is very similar to the
ALMA board that would work for EVLA.  Even if the samples are taken
every 2 ms, the MIB should be able to handle it - but the MIB would be
fairly busy if the samples have to be sent back to the control
building every 2 ms, rather than every 48 ms.