Microcontrollers Lab

Lab Objectives

The objective for this lab is to become familiar with the stack. This will be achieved through the simulation of a simple postfix notation (a.k.a., Reverse-Polish Notation or RPN) calculator.

Work Tasks

Step 1

Allocate your stack such that the stack is located in what we defined as the data section of RAM. Remember, we defined our data section with the label "PROG" using the ORG assembler directive. Use the LDS instruction to initialize your stack. Now, load the stack using a loop with the values shown below. After the stack is loaded, use the TSX command to transfer the SP to index register X and then to load accumulator A with $23 and accumulator B with $67 (HINT: take a look at the lecture on stacks).

Figure 3: Stack and its contents.

Step 2

Code the simple postfix notation calculator that performs the operation shown in Figure 4. This calculator will only perform one operation ((35) (5) (-2) + (10)x-(4)+). The infix expression of the operation to be performed is "35 + ((5 + -2) x 10) + 4". Don't worry about saving the operators on the stack. Always push values on the stack. However, when you reach an operator, pull the values off the stack into registers, perform the arithmetic operation, and push the result back on the stack according to Figure 4. Your final result should be 9 ($09) and should be on the top of the stack.

NOTE: the multiply instruction (MUL) multiplies two 8-bit numbers and returns a 16-bit number. In this case, only return the lower 8-bit as the result.

Step 3

Now take the postfix notation calculator a step further. Using a loop, branches, and the stack, create a postfix notation calculator that performs the +, -, x, and / operations, as shown in the example in CALC_IN. Add the variables below to the DATA section of your code. Use these variables to implement your calculator. The operations should be the machine opcode as follows:

+: $8A, -: $8B, x: $8C, and /: $8D. For example, if you want to use ABA to implement +, the value should be $18. Make sure to replace those ??s with what you want to use before you try to use the code. CALC_IN contains the variable with the operation to perform. Use conditional statements and your knowledge of the opcode to determine if there is an opcode, and if so which operation to perform. The values in CALC _IN below are initially 84/2*21+- and the result should be 1. Try another operation of your choosing by changing CALC_IN and discuss it in the methodology section of your report. Keep in mind you won't be able to use any values that are the same as the opcodes you are using, but any other value should work, including negative values.

CALC_IN FCB $08,$04,$8D,$02,$8C,$02,$01,$8A,$8B

HINTS: You will traverse the CALC_IN array in a similar fashion to lab 3. You will jump out of the array when an operator is found, pull two values off the stack, perform that particular operation, push the result onto the stack, and then return to the loop. Otherwise, you will just push the value on the stack.

NOTE: the divide instruction (IDIV) requires two 16-bit registers and returns a 16-bit value.

Only return the lower 8-bit as your result.

What to Turn In (Please read this carefully)

You are to put your code as text and screenshots into the "lab_4_template.docx" in the designated areas. This will be the file that you upload to TITANium as your submission. Provide your code as text, not an image. Points will be deducted if it is an image. You are then to take screenshots of your program in both CodeWarrior and terminal (i.e. on the Dragon board). The screenshot should show the relevant CPU registers and memory locations (NOTE: a convenient way of getting screenshots is to use the "snipping tool"). Do NOT crop the screenshot, for any credit I want a full screen screenshot of your computer screen including the task bar. Also you must answer the questions on the "lab_4_template.docx" file.

Attachment:- Lab_4_Instructions.pdf