EE 308

68HC12 Cycles

• 68HC12 works on 16 MHz clock
• A processor cycle takes 2 clock cycles - P clock is 8 MHz
• Each cycle takes 125 ns (1/8 $\mu$s) to execute
• An instruction takes from 1 to 12 cycles to execute

           ldab #10        ; LDAB:   1
    loop:  clra            ; CLRA:   1
           decb            ; DECB:   1
           bne  loop       ; BNE     3/1   (branch/no branch)
           swi             ; SWI     9

Program goes through loop 10 times. First 9 times it branches to loop, last time it does not.

Total number of cycles:

$1 + 9 \times (1 + 1 + 3)+ 1 \times (1 + 1 + 1) + 9 = 58$

58 cycles = 7.25 $\mu$s