Accomodating I2C and CAN in Hall D control system

[Elliott Wolin <wolin@jlab.org>]

Hall D Electronics:

Dear Gerard, Fernando, and friends,

I understand there will be a large number of I2C and CAN channels in Hall D.  In 
particular, one I2C channel per 24-channel preamp card, and one CAN channel per 
Cockroft-Walton base.  I understand there are other I2C channels (how many?);  are there 
additional CAN channels?

I don't know how many I2C and CAN channels can be daisy-chained on one I2C or CAN bus.  We 
may not want to daisy-chain too many channels, as then access to each device might take 
too long, e.g. when setting all the C-W high voltages prior to starting a run.

Further, I assume the detector and/or electronics budgets include whatever devices are 
needed to read out I2C and CAN, as the online budget contains just computers and network 
components.

Finally, I am concerned about mixing controls and DAQ data paths.  How are all the I2C 
devices connected and read out?  I hope not via VME in the DAQ crates, as this would 
interfere with the high-speed DAQ readout.

Controls data paths should be independent of DAQ data paths unless the controls data is 
intimately associated with DAQ (e.g. trigger scalers), i.e. only needed if DAQ is running.

Thanks,

				Sincerely,
					Elliott


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  Those raised in a morally relative or neutral environment will hold
		    no truths to be self-evident.
				

Elliott Wolin
Staff Physicist, Jefferson Lab
12000 Jefferson Ave
Suite 8 MS 12A1
Newport News, VA 23606
757-269-7365

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