64 lines
2.3 KiB
Plaintext
64 lines
2.3 KiB
Plaintext
From: jje@virtech.uucp (Jeremy J. Epstein)
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Newsgroups: alt.folklore.computers
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Subject: HCF instruction: from Principles of Operation
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Date: 25 Apr 90 13:19:07 GMT
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From IBM 360 Principles of Operations (aka POPS, POO, or POPL):
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Halt and Catch Fire
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HCF I (RR)
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-----------------
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| | |
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| FG | I |
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-----------------
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0 8 15
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A Start I/O to the system console is issued, using a CCW (channel command
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word) implemented in CPU circuitry. The CCW causes the console alarm
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to sound eight times. After return from the Start I/O, the system is placed
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in the stopped state. However, all pending interruptions are taken, and
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all I/O operations completed before entering the stopped state.
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The Power-on sequencer then operates, causing two actions. First, a 700
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volt, 200 ampere current is applied to all CPU circuitry excluding the
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power supply. Then, the same current is applied to main storage, causing
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the ignition of a small phosphorous flare located there.
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If the I field of the instruction is set to 4, the system also applies
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a 700 volt, 200 ampere current to the operator's chair.
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After the execution of this instruction, a customer engineer is required
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to restore the machine to its normal state.
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The power-on key is ineffective after the execution of this instruction.
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The emergency power-off pull switch is ineffective during the execution
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of this instruction.
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Condition code: The condition code remains unchanged.
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Program exceptions: Privileged operation.
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Programming notes:
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If the I field is anything other than 4, the normal version of the
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instruction is executed. This is the only instruction in the 360
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instruction set that causes transition from the operation to stopped
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state. Multiprogramming and timing dependent operations may be adversely
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affected.
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[My copy says it was written by David Holinstat (then of New Mexico
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Tech, now of Hewlett-Packard) and is dated spring 1977. It says
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that the writeup is based on an earlier version of unknown origin.]
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[The 360 POO was one of the best written manuals of its day. It was
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concise and complete. Jargon was kept to a minimum. It had its own
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unique style, due largely to being written by two people, unlike so
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many other manuals which are written by committee. Fans of the 360 POO
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will recognize the above as being in that style.]
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--
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