hi molly, i think most engineers and programmers that deal with fixed point numbers prefer to use fractional representation between -1 and +1, as then it doesn't make much difference how many bits the numbers have - they will all have the same range. a 16 bit number will range from -1 to +1, and so will an 8 bit number. the 16 bit number will have more bits to the right of the decimal point (15 bits to the right, and 1 bit to the left), vs an eight bit number will only have 7 bits to the right of the decimal point, so it won't be as precise.
if you prefer, you can rescale the 8 bit adc value to be an integer between -128 and +127. but if you do this, you might have to rescale things for the casper FFT and PFB or other casper blocks. i think it's probably best to keep the scaling as it is, between -1 and +1, as that's what casper blocks usually expect. best wishes, dan On Sun, Aug 9, 2020 at 7:31 PM 'Molly Smith' via casper@lists.berkeley.edu < casper@lists.berkeley.edu> wrote: > > Hello, > > I'm trying to get 8-bit real values from the katADC yellow block in > Simulink. I was wondering why the block outputs fixed 8.7 bit values > instead? I found the following explanation on one of the CASPER wikis but > I'm still confused. > > "The ADC block converts analog inputs to digital outputs. Every clock > cycle, the inputs are sampled and digitized to 8 bit binary point numbers > in the range of -1 to 1 and are then output by the ADC. This is achieved > through the use of two's-compliment representation with the binary point > placed after the seven least significant bits. This means we can represent > numbers from -128/128 through to 127/128 including the number 0. Simulink > represents such numbers with a fix_8_7 moniker. " > > Does it make sense to use a reinterpret block to convert it back to > 8-bits? > > Thanks, > Molly > > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To view this discussion on the web visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/d197809c-a3a9-4618-9b0f-bcafaaf4c1a7n%40lists.berkeley.edu > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/d197809c-a3a9-4618-9b0f-bcafaaf4c1a7n%40lists.berkeley.edu?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. To unsubscribe from this group and stop receiving emails from it, send an email to casper+unsubscr...@lists.berkeley.edu. To view this discussion on the web visit https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vGYMTxjsHuuBvPkf4JQ8uwobZXUDFhehCcogzLCPmirQg%40mail.gmail.com.
