So instead of writing the binary at the top of slide, we'll write assembly language statements to specify instructions in symbolic form. To program the Beta we'll need to load main memory with binary-encoded instructions.įiguring out each encoding is clearly the job for a computer, so we'll create a simple programming language that will let us specify the opcode and operands for each instruction. The Load/Store instructions access main memory, either loading a value from main memory into a register, or storing a register value to main memory.Īnd, finally, there are branches and jumps whose execution may change the program counter and hence the address of the next instruction to be executed. The yellow highlighting indicates instructions that use the second instruction format. The operands are either two values from the general-purpose registers, or one register value and a constant. The ALU instructions perform an arithmetic or logic operation on two operands, producing a result that is stored in the destination register. There are two instruction formats: one specifying an opcode and three registers, the other specifying an opcode, two registers, and a 16-bit signed constant. The 5-bit Ra, Rb, and Rc fields contain register numbers, specifying one of the 32 general-purpose registers. The 6-bit OPCODE field specifies the operation to be performed. This memory holds both data and instructions.īeta instructions are 32-bit values comprised of various fields. The datapath and control logic are connected to a large main memory with a maximum capacity of 2^32 bytes, organized as 2^30 32-bit words. In the CPU's control logic there is a special-purpose register called the program counter, which contains the address of the memory location holding the next instruction to be executed. In the CPU datapath there are 32 general-purpose registers, which can be read to supply source operands for the ALU or written with the ALU result. The Beta incorporates two types of storage or memory. In the previous lecture we developed the instruction set architecture for the Beta, the computer system we'll be building throughout this part of the course.
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