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In the x86 computer architecture, HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired. [1] Interrupts are signals sent by hardware devices to the CPU alerting it that an event occurred to which it should react.
The Motorola 6800 microprocessor was the first for which an undocumented assembly mnemonic HCF became widely known. The operation codes (opcodes—the portions of the machine language instructions that specify an operation to be performed) hexadecimal 9D and DD were reported and given the unofficial mnemonic HCF in a December 1977 article by Gerry Wheeler in BYTE magazine on undocumented ...
The XSAVE instruction set extensions are designed to save/restore CPU extended state (typically for the purpose of context switching) in a manner that can be extended to cover new instruction set extensions without the OS context-switching code needing to understand the specifics of the new extensions.
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.
For example, the NOP instruction translates to the opcode 0x90, and the HLT instruction translates to 0xF4. [3] There are potential opcodes without documented mnemonics, which different processors may interpret differently. Using such opcodes can cause a program to behave inconsistently or even generate exceptions on some processors.
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Normally the supporting chips provide the subroutine call command (CALL or RST), transferring control to the interrupt handling code. D1 reading (low level means writing) D2 accessing stack (probably a separate stack memory space was initially planned) D3 doing nothing, has been halted by the HLT instruction; D4 writing data to an output port
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.