title: immediate and program counter relative addressing
body: <p>i came across a code for an sic/xe machine....below are the lines which were a source of problem for me...</p>
  
  <pre><code>0003         LDB  #LENGTH  ;a
  0020         LDA  #3       ;b
  0033 LENGTH  RESW 1        ;c
  103C        +LDT  #4096    ;d
  </code></pre>
  
  <p>now it was given that 'a' will have an object code in which pc relative and immediate mode will be used....but b  will have just immediate mode....now as length is at 0033, so why use pc relative mode....and if it is imperative by convention that pc relative mode is too be used  so why not use both pc relative and immediate in 'b'?</p>