Op-code Mnemonic Function Example 001 LOAD Load the value of the operand into the Accumulator LOAD 10 010 STORE Store the value of the Accumulator at the address specified by the operand STORE 8 011 ADD Add the value of the operand to the Accumulator ADD #5 100 SUB Subtract the value of the operand from the Accumulator SUB #1 101 EQUAL If the value of the operand equals the value of the Accumulator, skip the next instruction EQUAL #20 110 JUMP Jump to a specified instruction by setting the Program Counter to the value of the operand JUMP 6 111 HALT Stop execution HALT A simple machine language

In the machine language above, notice that some of the operands include a # symbol. This symbol tells the CPU that the operand represents a number rather than a memory address. Thus, when the assembler translates an instruction with a # symbol, the resulting machine code will have a '1' in the position of the number bit. Also notice the central role that the Accumulator register plays. Nearly all the operations affect the value of this register since the Accumulator acts as a temporary memory location for storing calculations in progress. With our machine language defined, we are ready to take a look at some simple programs.

The first program is called Sum. This program adds the numbers stored in two memory locations. Mathematically, this program represents the formulas x = 2, y = 5, x + y = z where the variables x, y, and z correspond with the memory locations 13, 14, and 15 respectively. The instructions for the program are listed below. Read through the program, and then view the animation of this program by clicking the "View Animation" link.

 # Machine code Assembly code Description 0 001 1 000010 LOAD   #2 Load the value 2 into the Accumulator 1 010 0 001101 STORE  13 Store the value of the Accumulator in memory location 13 2 001 1 000101 LOAD   #5 Load the value 5 into the Accumulator 3 010 0 001110 STORE  14 Store the value of the Accumulator in memory location 14 4 001 0 001101 LOAD   13 Load the value of memory location 13 into the Accumulator 5 011 0 001110 ADD    14 Add the value of memory location 14 to the Accumulator 6 010 0 001111 STORE  15 Store the value of the Accumulator in memory location 15 7 111 0 000000 HALT Stop execution Sum program   [view animation]

The second program is called Count. This program counts up to a number specified by the programmer in the first instruction. Notice that this program incorporates a loop construction by using the JUMP and EQUAL instructions. Every time the value in the Accumulator is incremented, the count is tested to see if it has reached the specified amount. Read through the program, and then view the animation of this program by clicking the "View Animation" link.

 # Machine code Assembly code Description 0 001 1 000101 LOAD   #5 These two operations set the count value to five 1 010 0 001111 STORE  15 2 001 1 000000 LOAD   #0 Initialize the count to zero 3 101 0 001111 EQUAL  15 Test to see if count is complete; if yes, skip next instruction and go to instruction 5; if no, go to next instruction 4 110 1 000110 JUMP   #6 Set Program Counter to 6 5 111 0 000000 HALT Stop execution 6 011 1 000001 ADD    #1 Increment the count in the Accumulator 7 110 1 000011 JUMP   #3 Set Program Count to 3 Count program   [view animation]

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