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