On Thursday, April 07, 2016 3:16 AM, Ian Abbott wrote:
> On 06/04/16 19:06, H Hartley Sweeten wrote:
>> The "hc" type boards have 64 analog input channels with a 64 entry queue.
>> All the others have 16 channels and a 256 entry queue.
>>
>> Currently the boardinfo 'qram_len' is used to initialize the subdevice
>> 'n_chan' and 'len_chanlist'. This works for the 64 channel boards but
>> sets the 'n_chan' wrong for the 16 channel boards.
>
> I think the 256 QRAM positions is to allow use with a set of EXP-1800
> boards, each of which can multiplex one of the single-ended inputs of
> the DAS-1800 series into 16 channels. According to the user's guide,
> they can be daisy chained to provide up to 256 channels.
>
> Datasheet:
>
> http://www.tek.com/sites/tek.com/files/media/media/resources/exp-1800_ds.pdf
>
> User's Guide download page (need to fill in contact info!):
>
> http://www.tek.com/manual/exp-1800-users-guide-92160b-manual
>
>
> So it's probably best to leave the number of channels alone.
I wasn't aware of the EXP-1800 expansion board.
I get a 403 Forbidden error when I try to download the user's guide. Do you
have a copy you can send to me?
The EXP-1800 support looks like it will need additional changes to the driver
in order to work correctly. According to the data sheet:
1) all board input channels must be configured as single-ended,
EXP-1800 inputs can be single-ended or differential. Not sure how
the board needs to be programmed to achieve this.
2) only gains of 1 and 50 are selectable on a per-channel basis
3) resolution is 12-bit, not clear how this works on a 16-bit board
4) max ai speed depends on the EXP-1800 gain not the board
gain 1 = 312kHz sample rate
gain 50 = 150kHz sample rate
5) gain must be the same on all channels and the boards gain must be 1
Additionally, it's not clear how the channel mapping works for each
EXP-1800 connected to a board input channel.
I think it's better to set the number of channels to 16 and just support
the on-board analog inputs for now. Once the EXP-1800 support is
figured out it can be added.
Regards,
Hartley
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