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The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. [2] It is the last 8-bit microprocessor developed by Intel. It is software-binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added interrupt and serial input/output features.
Control unit has access to the instruction memory in order to fetch the instructions to be executed. In order to allow the executed programs to transfer the execution (jump) to an arbitrary position in the executed program, control unit provides control flow operations.
A program in machine code consists of a sequence of machine instructions (possibly interspersed with data). [1] Each machine code instruction causes the CPU to perform a specific task. Examples of such tasks include: Load a word from memory to a CPU register; Execute an arithmetic logic unit (ALU) operation on one or more registers or memory ...
This effectively 'stores' the result without an explicit store instruction. CISC — Often machines are limited to one memory operand per instruction: load a,reg1; add b,reg1; store reg1,c; This requires a load/store pair for any memory movement regardless of whether the add result is an augmentation stored to a different place, as in C = A+B ...
The instruction set architecture (ISA) that the computer final version (SAP-3) is designed to implement is patterned after and upward compatible with the ISA of the Intel 8080/8085 microprocessor family. Therefore, the instructions implemented in the three SAP computer variations are, in each case, a subset of the 8080/8085 instructions.
The effect is to transfer control to the instruction whose address is in the specified register. Many RISC machines, as well as the CISC IBM System/360 and successors, have subroutine call instructions that place the return address in an address register—the register indirect addressing mode is used to return from that subroutine call.
The processor executes a program by fetching the instructions from memory and executing them. Usually the processor execution speed is much faster than the memory access speed. Instruction queue is used to prefetch the next instructions in a separate buffer while the processor is executing the current instruction.
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.