Heres a little tip:
Instructions Per Second = Crystal (in mhz) * 1,000,000 / 4
or (they are the same)
Instructions Per Second = Crystal (in mhz) * 250,000
EXAMPLE: 20Mhz * 250,000 = 5,000,000 IPS (instructions per second)
Knowing that we can get how long each instruction takes. We have o divide the 1 by IPS
EXAMPLE...
X = 1 / 5,000,000 = 0.0000002 Seconds (s) Per Cycle
Note the .0 Places. The "," is there only as a visual helper. You rather see .000001 or .000,001. They are the same but easier to see the places with a comma.
.001 - .999 = mS (3 places) (Thousands)
.000,001 - .000,999 = uS (6 places) (Hundred Thousands)
.000,000,001 - .000,000,999 = nS (9 places) (Hundred Millions)
X falls into the nS range being .000,000,2 so we have to multiply it by its places. So:
X = .000,000,2 * 1,000,000,000 = 200nS Per Instruction
If im wrong tell me now lol