Erik,

First of all I want to say that I am not an expert in PIC micros. I have used the 8051 family MCUs for many years and I feel comfortable with them. My knowledge about PICs is esentially based in books and the interpretation of block diagrams.

In the PIC16C5X block diagram I find a dedicated 9-11 bits path from the PC to the program memory. The instructions come out from this memory (are fetched) via another dedicated path (12 bits wide) and go into the instruction register, whose outputs are connected directly to the instruction decoder.
I supposse that a set of control signals are generated here that perform the tasks corresponding to that instruction (execution). In addition, the address involved is sent to the register file.
For example, in an arithmetic instruction, the contents of a register (some address in the register file) can be sent to the ALU via the data bus (8 bits wide) and operate with the accumulator (work register).

I remark the existence of two different paths: one 12-bits wide for the ROM output (instructions or literals) and other 8-bits wide for the SRAM (register file) output.

I admit that I don't know how the real internal activity is performed. I simply think that the buses' structure is suitable for a true Harvard operation.

I am specially interested in this theme beacuse I have to explain this concepts as an assistant lecturer in my University. So I am happy to receive all the information and opinions about microcontrollers structural peculiarities. By the way, we use MCUs of the 8051 familiy in our laboratories. We dedicate one lecture to speak about other microcontrollers.

Regards,

Alfredo del Rio.