In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

When looking at the instruction set of a processor/controller, in most cases, you will find some instructions that make you think "what are these good for?". Don't worry, one day, you will be glad that they are there.

For example, when I started with the SX I was wondering about the SKIP instruction, asking me why should I ever use an instruction that always skips the next one, I could always leave out the SKIP and the next instruction.

Later, when dealing with code to handle the I²C protocol, I found a good use for SKIP: To handle the bus timing, you sometimes need a delay routine for a certain period - let me call it T1 here, but sometimes you need to delay twice as long, i.e. T * 2, or T2. Here is a code snippet for this using the SKIP instruction:

DelayT1
  mov w, #Delay
  SKIP
DelayT2
  mov w, #Delay * 2
  mov  DelayCounter, w
:Loop
  decsz DelayCounter
  jmp :Loop
ret

As you can see, the SKIP is used here to skip the initialization of W for the longer delay in case DelayT1 is called. Using SKIP instead of a JMP requires two clock cycles instead of three - not a big deal but "tricky" :-) .

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