Introduction to DSP - DSP processors: Texas processors

The Texas TMS320C25 is quite an early design. It does not have a parallel multiply/add: the multiply is done in one cycle, the add in the next and the DSP has to address the data for both operations. It has a modified Harvard bus with only one data bus, which sometimes restricts data memory accesses to one per cycle, but it does have a special 'repeat' instruction to repeat an instruction without writing code loops

The Texas TMS320C50 is the C25 brought up to date: the multiply/add can now achieve single cycle execution if it is done in a hardware repeat loop. It also uses shadow registers as a fast way to preserve registers when context switching. It has automatic saturation or rounding (but it needs it, since the accumulator has no guard bits to prevent overflow), and it has parallel bit manipulation which is useful in control applications

The Texas TMS320C30 carries on some of the features of the integer C25, but introduces some new ideas. It has a von Neuman architecture with multiple memory accesses in one cycle, but there are still separate internal buses which are multiplexed onto the CPU. It also has a dedicated DMA controller.

The Texas TMS320C40 is similar to the C30, but with high speed communications ports for multiprocessing. It has six high speed parallel comm ports which connect with other C40 processors: these are 8 bits wide, but carry 32 bit data in four successive cycles.