assembly - 用 68k 汇编语言生成随机字母

Question

我被困在我的作业上，它告诉我在 A 到 J 范围内生成一个随机字母我知道我应该使用 ascii 表，但是如何在 easy68k 中编写代码？我已经尝试了一切，但我似乎只能生成一个随机数，而不是一个字母。请帮忙

Answer 1

From a quick check of the list of "trap tasks" it seems task 8 returns current time in milliseconds. You could/should use this as a seed to a proper random number generator, but for now let's just run with that number alone.

I'd do something like:

random_character:
  moveq.w #8,d0
  trap    #15   ; returns ms in d1
  divu.w  #10,d1
  moveq.w #0,d1 ; clear lower word
  swap    d1    ; get remainder, i.e. compute d1 % 10
  addi.w  #'A',d1
  rts

Something like that should work. Of course, if you call it too quickly you will get the same letter until the clock has progressed.