Re: Accomodating I2C and CAN in Hall D control system

["Fernando J. Barbosa" <barbosa@jlab.org>]

Hall D Electronics:

Hi Elliott,

In I2C, the maximum number of serial devices on the same serial com 
lines (clock and data) depends on the devices to be employed. The 
temperature sensors that we use on the preamp cards provide the I2C with 
support for up to 9 devices. However, because of the LV power 
distribution, two cards share the same cable out of the distribution 
box. A LV distribution box (there will be 4 for the FDC, for example) 
will then split the LV power and I2C communications. Although it is 
still early to have a final design on the LV distribution system, my 
plan is to have an Ethernet-to-I2C interface (cheap) on the distribution 
box (RS232 or RS422 would work also).

The CWs are similarly distributed in factors of 16 with CAN control. 
Again, Ethernet-to-CAN interfaces are readily available and cheap.

The same philosophy for controls and monitoring applies to the crates, 
the HV and the LV supplies and it can be easily extended to any other 
monitoring function, such as temperature/humidity. Clearly, there is 
complete decoupling from the DAQ data paths and VME would just be too 
expensive for these types of functions.

I should mention that I have distributed all this information through 
documents and/or reviews. I apologize in advance but I have not had the 
time to complete a document I am working on regarding this issue. It 
should be out soon.

Regards,
Fernando



Elliott Wolin wrote:
> 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
>
>
> ================================================================================ 
>
>
>
>  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
>
> ================================================================================ 
>