Assembly Language Programming - Fundamentals of Computer Organization and Architecture - page 39

TABLE 3.1 Instruction Set of the Simple Processor

Operation code Operand Meaning of instruction

0000 Stop execution

0001 adr Load operand from memory (location adr) into AC

0010 adr Store contents of AC in memory (location adr)

0011 Copy the contents AC to DR

0100 Copy the contents of DR to AC

0101 Add DR to AC

0110 Subtract DR from AC

0111 And bitwise DR to AC

1000 Complement contents of AC

1001 adr Jump to instruction with address adr

1010 adr Jump to instruction adr if AC ¼ 0

We assume that our simple processor supports three types of instructions: data
transfer, data processing, and program control. The data transfer operations are
load, store, and move data between the registers AC and DR. The data processing
instructions are add, subtract, and, and not. The program control instructions are
jump and conditional jump. The instruction set of our processor is summarized in
Table 3.1. The instruction size is 16 bits, 4 bits for the operation code and 12 bits
for the address (when appropriate).

Example 1 Let us write a machine language program that adds the contents of
memory location 12 (00C-hex), initialized to 350 and memory location 14 (00E-hex),
initialized to 96, and store the result in location 16 (010-hex), initialized to 0.
The program is given in binary instructions in Table 3.2. The first column gives
the memory location in binary for each instruction and operand. The second column

TABLE 3.2 Simple Machine Language Program in Binary (Example 1)

Memory location
(bytes)

Binary instruction Description

0000 0000 0000 0001 0000 0000 1100 Load the contents of location 12 in AC

0000 0000 0010 0011 0000 0000 0000 Move contents of AC to DR

0000 0000 0100 0001 0000 0000 1110 Load the contents of location 14 into AC

0000 0000 0110 0101 0000 0000 0000 Add DR to AC

0000 0000 1000 0010 0000 0001 0000 Store contents of AC in location 16

0000 0000 1010 0000 0000 0000 0000 Stop

0000 0000 1100 0000 0001 0101 1110 Data value 350

0000 0000 1110 0000 0000 0110 0000 Data value is 96

0000 0001 0000 0000 0000 0000 0000 Data value is 0