I just looked through the attenuator data sheet - there are no settling time specifications, but I'm sure whatever it is, it will be dominated by the time taken to set up the registers.
-Francois On Mon, Mar 19, 2012 at 9:05 AM, Andrew Martens <[email protected]> wrote: > Hi Nimish > > > To be more specific, we would like to change the attenuation in the > > KatADC RF front end every 20 ms and we can allow up to 1 ms of dead > > time/settling time. Do you think this can work? > > Just had a quick look through the IIC controller. Seems to need to write > around 12 words, each 8 bits in size, using a 100kHz clock. This equates > to around (10us * 12 * 8) ~= 1ms to change attenuation values so 20ms > should be enough. I am not sure about the settling time of the > programmable attenuator. > > > A related question is how to change this attenuation. I tried using a > > software register connected to atten* inputs of the KatADC yellow > > block, but the design would not compile. I have not got time to check > > at what stage it fails, but I can look into that. I got the design > > compiled by connecting just the "constant" blocks to these inputs. Is > > it first of all allowed to have a software register there? If not, > > what would be the way to change this attenuation dynamically? > > > We have software registers that control this value in designs here. If > software registers work in other parts of your design, they should work > here - there is nothing special about those ports. You can also set > these values in software from the PPC if that is easier, the IIC > controller can be accessed from the PPC. > > Regards > Andrew > > > -- Francois Kapp Sub-system Manager Digital Back End meerKAT SKA South Africa Third Floor The Park Park Road (off Alexandra Road) Pinelands 7405 Western Cape South Africa Latitude: -33.94329 (South); Longitude: 18.48945 (East). (p) +27 (0)21 506 7300 (p) +27 (0)21 506 7360 (direct) (f) +27 (0)21 506 7375 (m) +27 (0)82 787 8407
