Yuping Dong


Discussion created by Yuping Dong on Oct 27, 2009
Latest reply on Oct 29, 2009 by kef

Hi there,


Does anyone know how to calculate the execution cycle for XC68HC912?

I saw there are "access details" for each instruction from the CPU12 reference manual. I can understand some of them, like "I" is reading indirect pointer, "r" is 8-bit data read. But I'm confused with the sequence of these letters. I thought "P" and "O" were for fetching instructions, so I thought the access details should always begin with "P" or "O". But there are exceptions. For example, STAA, the access details for M68HC12 are:


STAA opr8a                 Pw

STAA opr16a              wOP

STAA oprx0_xysp          Pw

STAA oprx9,xysp        PwO

STAA oprx16,xysp      PwP

STAA [D,xysp]         PIfPw

STAA [oprx16,xysp]  PIPPw


Does anyone know which direction is the instruction execution going? From right to left or left to right? But either direction has some instructions with "w" first. "w" is 8-bit data write. Why is there a write before even fetching the instruction?


Thanks a lot in advance for any inputs!!