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Assembly Language

input/output instructions

    This web page examines input/output instructions in assembly language. Specific examples of instructions from various processors are used to illustrate the general nature of assembly language.

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• table of contents for assembly language section
• input/output
• MIX devices
• further reading: books on assembly language
• related software
• further reading: websites

input/output

    Input/Output (I/O) instructions are used to input data from peripherals, output data to peripherals, or read/write input/output controls. Early computers used special hardware to handle I/O devices. The trend in modern computers is to map I/O devices in memory, allowing the direct use of any instruction that operates on memory for handling I/O.

• IN Input; MIX; initiate transfer of information from the input device specified into consecutive locations starting with M, block size implied by unit
• OUT Output; MIX; initiate transfer of information from consecutive locations starting with M to the output device specified, block size implied by unit
• IOC Input-Output Control; MIX; initiate I/O control operation to be performed by designated device
• JRED Jump Ready; MIX; Jump if specified unit is ready (completed previous IN, OUT, or IOC operation); if jump occurs, J-register loaded with the address of the instruction which would have been next if the jump had not been taken
• JBUS Jump Busy; MIX; Jump if specified unit is not ready (not yet completed previous IN, OUT, or IOC operation); if jump occurs, J-register loaded with the address of the instruction which would have been next if the jump had not been taken

MIX devices

    Information on the devices for the hypothetical MIX processor’s input/output instructions.

unit number	peripheral	block size	control
t	Tape unit no. i (0 i 7)	100 words	M=0, tape rewound; M < 0, skip back M records; M > 0, skip forward M records
d	Disk or drum unit no. d (8 d 15)	100 words	position device according to X-register (extension)
16	Card reader	16 words
17	Card punch	16 words
18	Printer	24 words	IOC 0(18) skips printer to top of following page
19	Typewriter and paper tape	14 words	paper tape reader: rewind tape

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    Last Updated: February 21, 2001

    Created: February 21, 2001 (from machcode.htm)

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