ModuleWare Reference Guide - Hornad

Bus Tapper (tap)Bit Manipulation PartsBus Tapper (tap)This part taps bits from the input bus din and places them in the output busdout.The parameter start_at is a zero-based index that defines the location of thefirst bit in din that will be copied to the least significant bit of dout. The bitsof dout are filled from the bits of din in increasing order until either dout has been filled oruntil there are no more bits in din. If there are not enough bits in din to fill up dout, theremaining bits of dout are filled with X.FunctionFor every bit i of the bus:dout(i) = din(start_at+ i)= Xif start_at + i < width of port dinotherwiseTruth TableExample tapping 3 bits from a 7-bit bus:Table 5-23. Bus Trapper Truth Tabledin start dout00100111 0 1110100111 1 0110100111 2 0010100111 3 1000100111 4 0100100111 5 X010100111 6 XX0ParametersTable 5-24. Bus Trapper ParametersParameter Values DefaultdindoutPort width (must be > 0)Port width (must be > 0)start_at Start location, must be >= 0 and < width of port din 0AutomaticAutomaticDesign Rule Checks• An error is issued if the width of any port cannot be determined or if parameter start_at isnot greater than or equal to 0 and less than the width of port din.• A warning is issued and HDL generation fails for this part if any ports are not connected.ModuleWare Reference Manual, Library Version 1.9 91September 18, 2008