about 'DSPB_Type' and 'double' in dspbuilder

Before 7.1, there was not much difference between the two blocks. This was when DSP Builder just used double precision floating point numbers for its signal values. Consequently DSP Builder couldn't work properly with signals wider than 51 bits. (The width of the mantissa).

With 7.1 however, DSP Builder supported arbitrary precision signals using its own type, DSPB_TYPE. This type is not recognised by ordinary Simulink blocks so the Input and Output blocks act as a bridge converting the types at the borders of the system.

The Altbus block is then just an internal conversion block. For instance, it can convert from a signed number to an unsigned number or to a fractional number. It can also be used to change the bit-width of a signal.