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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 default OperandSize and AddressSize to use for each instruction is given by the D bit of the segment descriptor of the current code segment - D=0 makes both 16-bit, D=1 makes both 32-bit. Additionally, they can be overridden on a per-instruction basis with two new instruction prefixes that were introduced in the 80386: 66h: OperandSize ...
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 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.
It added a signed overflow bit to the status register (bit 3). Status register bits 4 and 5 provided read-only access to the high 2 bits of the 10-bit program counter. The instruction set is mostly the same as the 12-bit PIC with the address field enlarged. However, the 8-bit immediate instructions gain an additional opcode bit.
Using the software interrupt 21h instruction to call the MS-DOS operating system for output to the display – other samples use libc's C printf() routine to write to stdout. Note that the first example, is a 30-year-old example using 16-bit mode as on an Intel 8086. The second example is Intel 386 code in 32-bit mode.
D3 doing nothing, has been halted by the HLT instruction; D4 writing data to an output port; D5 reading the first byte of an executable instruction; D6 reading data from an input port; D7 reading data from memory; 4: D5 5: D6 6: D7 7: D3 8: D2 9: D1 10: D0 11: −5 V — The −5 V power supply.
For conventional binary computers, machine code is the binary representation of a computer program which is actually read and interpreted by the computer. 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.