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!!