The High Voltage Card

The data is shifted in serially through six 8-bit registers. The data then comes out via HV_DATA_OUT. Thus bits of (serial) data are in general needed. However, not all 48 bits are used. There are bits used with the remaining lines left unconnected. If we decide that we want to shift in 48 bits every time we perform a function then the programming is easy.

• The first 3 bits (47..45) are unused.

• Bits (40..44) choose which of the 32 PMT base currents is monitored. Bit 44 is the 2**5 bit,,bit 40 is the 2**0 bit.

• Bits (36..39) are also unused

• Bits (32..35) are on/off for whichever HV relay is to be turned on/off. There are 4 relays for 32 channels. Bit 35 turns on relay 4, bit 34 turns on relay 3 ... bit 32 turns on relay 1.

• Bits (0..31) are the 32 bits which enable charge injection tests on each of 32 channels. Bit 31 controls channel 31 (PMT 32),,bit 0 controls channel 0 (PMT 1).

  The system is set up so that many things can be turned on/off at once. The only exception is the base current measurement for which only one channel can be monitored at a time.

• HVLOAD is enabled when the proper serial bits get to their proper destinations.

An example:
-----------
NOTE: bit 47 is shifted in first and bit 0 last in this naming scheme. 
      i.e. time runs as shown.

     TIME ----------------------------------------------------->

              |-|--> Unused (45..47)
              |-|
              |-| |---|--> Binary enable PMT base current measurment
              |-| |---|
              |-| |---| |--|--> Unused (36..39)
              |-| |---| |--|
              |-| |---| |--| |--|--> Enable some of 4 relays on HV card
              |-| |---| |--| |--|
              |-| |---| |--| |--| |--> Choose which channel to charge inject
              |-| |---| |--| |--| |-->
              |-| |---| |--| |--| |-->
        Bit:  444 44444 3333 3333 3322222222221111111111
              765 43210 9876 5432 10987654321098765432109876543210

      HVLOAD: 000 00000 0000 0000 000000000000000000000000000000001

        Data: 000 10010 0000 1010 10000100000000000001000010000000
                    |        | |  |    |             |    |
                    |        | |  |    |             |    |---> Chan. 7 (CHG INJ)
                    |        | |  |    |             |   
                    |        | |  |    |             |--> Chan. 12 (CHG INJ)
                    |        | |  |    |
                    |        | |  |    |--> Chan. 26 (CHG INJ)
                    |        | |  | 
                    |        | |  |--> Chan. 31 (CHG INJ)
                    |        | |
                    |        | |--> Enable Relay 2
                    |        |
                    |        |--> Enable Relay 4
                    |      
                    |--> 10010 => Ch 18 (PMT 19) base current measurement

Note: HVLOAD wasn't enabled until all 48 bits (0..47) had been shifted through. This is not necessary. If we wanted to only enable charge injection in channel 0, we'd only need 1 bit shifted in and then enable HVLOAD. I think we should stay away from this however. It would get confusing and increase the probability of error.