basic (stupid ?) filtering questions

Hi all,

I.m playing with a self-made FIR filter (no fir compiler used).

I have read the theory, but the devil is in the implementation, as they say :-P

my ADC generates 8 bits values [0-255].

can I just feed these into the filter or do I need to "center the signal around 0", i.e. make sure that the signal value on average is 0 for the

calculations to work ?

(this would require signed values...)

second question, assuming I need signed values:

is this correct ?

reg [7:0] unsignedval;

reg signed [7:0] signedval;

// from unsigned to signed

signedval <= $signed(unsignedval - 8'd128);

// and back :

unsignedval <= $unsigned(signedval + 8'sd127 + 8'sd1);

(since 8'sd128 does not fit in 8 bits 2scomplement)

thanks for getting me up to speed !

ps I built my own filter in order to avoid the added complexity and choice offered by the FIR compiler.