TOY EXERCISES

READING 
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TOY notes.
Lecture notes for TOY.
King, 20.1 (bitwise operators)


EXERCISES
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For each of the following TOY programs, suppose that TOY
is started at 10 with the given hex numbers loaded into memory.  
For each problem, give the contents of R1 and R2 when the 
machine halts.

 1.
      10: B111
      11: B210
      12: 2112
      13: 0000

 2. 
      10: 9111
      11: 9210
      12: 2112
      13: 0000


 3.
      10: B101
      11: B20C
      12: B301
      13: 1111
      14: 2223
      15: 7213
      16: 0000
 4.
      10: B100
      11: B201
      12: B304
      13: B405
      14: 1112
      15: 7414
      16: 7313
      17: 0000

 5. Suppose one wanted to increase the TOY machine memory to 2048 
    16-bit words, instead of 256.  What is the major problem that would 
    need to be addressed?














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		       ANSWERS TO TOY EXERCISES


 1. R1 = 0001,  R2 = 0010

 2. R1 = 00FF,  R2 = 9111

 3. R1 = 0040,  R2 = 0000

 4. R1 = 0014,  R2 = 0001

 5. Need 11 bits to address the 2^11 = 2048 words, so "load" and "store" 
    instructions (for example)  have to be redesigned, since they need 
    4 bits for the opcode, 3 bits for the register, and 11 bits for the 
    address, 2 bits too many to fit into a 16-bit word.