Post by thread:[PIC] Microcode vs. millicode

Does anyone know what the difference between microcode and millicode is as far as chips and cpu are concerned? Do PIC's use microcode? They were talking about this in an IBM mainframe discussion group and I didn't quite know what it all meant. If anyone knows you guys do. (-: Lindy

> > Does anyone know what the difference between microcode and millicode is as > far as chips and cpu are concerned? I'd say millicode is a specific term coined by IBM to define something between machine code and microcode. Do PIC's use microcode? Given the margins on microcontrollers, I would estimate they don't (especially not the <18F models). Microcode would increase the chip area, not not provide any significant feature improvements: microcode is more useful if your instruction set is more fluid. They were talking about this in an IBM mainframe discussion group and I > didn't quite know what it all meant. If anyone knows you guys do. (-: You might consider using google, there are some good articles on millicode directly available on the Internet. Lindy Greetings, Maarten Hofman.

Thanks Maarten. I did find some good info on millicode. But for microcode I wasn't specific enough to get a good response from Google. {Original Message removed}

> Does anyone know what the difference between microcode and millicode is as > far as chips and cpu are concerned? > millicode sounds like a marketing term to me. wikipedia is useful for microcode: http://en.wikipedia.org/wiki/Microcode Cheers, Bob

It is quite unlikely that any PIC uses microcode in any normal sense. Microcode generally is used to run a 'microprogram' that interprets the traditional machine language of the processor. This implies that at least some instructions are probably going to take more than one cycle. Of course, this doesn't happen on a PIC (multicycle instructions are really just pipeline 'stalls' required to pick up the next prefetched instruction. Given the simplicity and orthoganality of the PIC instruction set I am nearly sure that it is decoded with simple combinatorial logic. Bob Ammerman RAm Systems {Original Message removed}

On Tue, 30 May 2006, Lindy Mayfield wrote: > Does anyone know what the difference between microcode and millicode is as far as chips and cpu are concerned? > > Do PIC's use microcode? PICs do not use microcode. They are about as 'straight through' as it goes. Peter