第七讲 单片机系统设计过程及应用实例new(待更新).ppt

习题 1 PIC系列单片机有哪几种指令？共有多少条？ * MOVF or “Move F” is another very popular instruction. This instruction lets you take a value from any file register and copy it to W. You can also send the result back to the same register you read it from, and this will affect the Z flag, making it easy to test for 0 without writing to other locations. In general though, you will see it paired with MOVWF, as values are moved between W and various file register RAM locations. * You can do some impressive things with some instructions. This instruction looks a lot like DECF, but it does more. “SZ” means “Skip if Zero” so, this instruction “DECrements Fand Skips if Zero”. The question to answer is what is skipped - and that is the next instruction. The best way to understand the use of this instruction is to look at the example shown here: The loop shown with this instruction has a GOTO as the next instruction. This loop will run over and over again, until CNT becomes 0. At that point the GOTO is skipped, and the code continues. Don’t worry if you don’t completely understand it at this point, we will be reviewing it again more later. * There are plenty of other instructions available to you. This one is RRF which is “Rotate Right though Carry”. It simply shifts all the bits to the right. The Carry flag supplies the leftmost bit, and the rightmost bit then goes into the carry flag. Its very useful for multiplying by 2, testing bits (with bit test instructions used afterwards), or for creating serial routines in software. * Lets take a quick look at the encoding of bit-oriented operations. Remember, these instructions all work on a file register, indicated by the “f”s, but they operate on only one bit (0 to 7) in that register, which is encoded by the “b”’s. You can bit clear, set, test, etc and we will look at these next. * Here is a bit clear instruction. BCF bit clears the bit requested by the code. For example BCF FSR,4 clears bit 4 of FSR as you can