Arrays and ArrayLists - Java: How to Program Early Objects - page 309

Operation code Meaning

Input/output operations:
final int READ = 10 ;

Read a word from the keyboard into a specific location in memory.

final int WRITE = 11 ;

Write a word from a specific location in memory to the screen.

Load/store operations:
final int LOAD = 20 ;

Load a word from a specific location in memory into the accumulator.

final int STORE = 21 ;

Store a word from the accumulator into a specific location in memory.

Arithmetic operations:
final int ADD = 30 ;

Add a word from a specific location in memory to the word in the
accumulator (leave the result in the accumulator).

final int SUBTRACT = 31 ;

Subtract a word from a specific location in memory from the word in
the accumulator (leave the result in the accumulator).

final int DIVIDE = 32 ; Divide a word from a specific location in memory into the word in

the accumulator (leave result in the accumulator).

final int MULTIPLY = 33 ;

Multiply a word from a specific location in memory by the word in
the accumulator (leave the result in the accumulator).

Transfer-of-control operations:
final int BRANCH = 40 ;

Branch to a specific location in memory.

final int BRANCHNEG = 41 ;

Branch to a specific location in memory if the accumulator is negative.

final int BRANCHZERO = 42 ;

Branch to a specific location in memory if the accumulator is zero.

final int HALT = 43 ;

Halt. The program has completed its task.

Fig. 7.33 | Simpletron Machine Language (SML) operation codes.

The first SML program (Fig. 7.34) reads two numbers from the keyboard and computes and
displays their sum. The instruction +1007 reads the first number from the keyboard and places it
into location 07 (which has been initialized to 0). Then instruction +1008 reads the next number
into location 08 . The load instruction, +2007 , puts the first number into the accumulator, and the
add instruction, +3008 , adds the second number to the number in the accumulator. All SML arith-
metic instructions leave their results in the accumulator. The store instruction, +2109 , places the result
back into memory location 09 , from which the write instruction, +1109 , takes the number and dis-
plays it (as a signed four-digit decimal number). The halt instruction, +4300 , terminates execution.

Location Number Instruction

00 (Read A)

+1007

01 (Read B)

+1008

02 (Load A)

+2007

03 (Add B)

+3008

04 (Store C)

+2109

Fig. 7.34 | SML program that reads two integers and computes their sum. (Part 1 of 2.)