Homework 3
UCR EE/CS120B: Introduction to Embedded Systems
Winter Quarter 2002, Prof. Frank Vahid
Due Friday May 10 by 2:00 p.m. to Vahid's office, Surge 328
   (put under door if door is closed)

1. Write assembly code, using the instruction set provided in ESD Fig 3.7,
   for the following:

   // assume x is M[3]
   // assume y is M[11]

   if (x == y) {
      x = 0;
   }
   else {
      y = 0;
   }

2. Repeat problem 1 using the 8051 instruction set.

3. Write 8051 assembly code that sends data to another device as
   follows. Initialize P1.1 to 0. Write the data R0 to P0. 
   Set P1.1 to 1. Wait for at least 8 clock cycles. Set P1.1 to 0.
   Assume the 8051 is a "turbo" 8051 using 4 cycles per instruction,
   non-pipelined.

4. Design a 16-bit processor, having a Harvard architecture (separate
   program and data memory), able to support up to 32 instructions.
   It has 2K of data memory, 64K of program memory, 32 registers,
   and an accumulator.  It supports the following instructions:
      * A = M(direct)
      * M(direct) = A
      * Rn = A
      * A = Rn
      * A = immediate
      * A = A + Rn
      * A = A - 1 (decrement)
      * Jump to PC+offset if A is 0 (offset up to +1024 or -1023)
      * Jump to PC+offset unconditionally
   (a) Define an instruction set using pneumonics. Also show the binary 
       representation of the instruction. 
       (i.e., do what was done in ESD Fig 3.7). Note
       that this is an accumulator-based machine -- the accumulator is
       involved in all memory transfers and arithmetic operations, and
       is implicit in those instructions. I.e., do NOT include a field
       for the accumulator.
   (b) Describe the processor as an FSMD, then create a datapath plus an 
       FSM, and finally implement a control unit having a controller that 
       uses a state-register plus ROM (show the ROM contents).
   (c) Comparing your processor to that of Fig 3.7, list the main
       advantage and disadvantage of an accumulator based machine
       (above) versus one without an accumulator (Fig 3.7)
       
   We recommend you do this problem using a word processor or other
   electronic capture tool, since drawing it out on paper may 
   become cumbersome.

5. (a) Write an assembly program that uses your processor to compute 
   the following.  Assume w is M[1], x is M[2], y is M[3]. Assume you
   must update x and w in memory.

   while (w != 0)
   {
      x = x + y;
      w = w - 1;
   }

   (b) Translate the first three instructions of your program into binary.