Browse Prior Art Database

Monitor Mode

IP.com Disclosure Number: IPCOM000096933D
Original Publication Date: 1962-Feb-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Montgomery, HC: AUTHOR

Abstract

Correction of a computer program sometimes requires awareness of the exact sequence of operations leading up to the error. In long programs where there is some repetition and branching, an error prehistory necessarily involves a listing of several steps in the sequence which terminated in the error. In monitor mode, the computer automatically logs the address of each instruction as it executes the instruction. Printout of the program addresses, performed just after detection of the error, thus includes, as its terminal group of instruction addresses, an exact prehistory of the error.

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Monitor Mode

Correction of a computer program sometimes requires awareness of the exact sequence of operations leading up to the error. In long programs where there is some repetition and branching, an error prehistory necessarily involves a listing of several steps in the sequence which terminated in the error. In monitor mode, the computer automatically logs the address of each instruction as it executes the instruction. Printout of the program addresses, performed just after detection of the error, thus includes, as its terminal group of instruction addresses, an exact prehistory of the error.

Computer 1 includes instruction address register 2, called instruction counter. This counter, during usual sequences, is incremented +1 during the execution of each instruction. A branch instruction, however, can alter the instruction address to an arbitrary value.

During ordinary operations of computer 1, the contents of instruction counter 2 are set into memory address register 3 to reference storage unit 4. Storage unit 4 reads out to memory data register 5 to secure an instruction for program unit 6. This unit 6 controls memory references to data and causes arithmetic unit 7 to execute the desired instruction upon the data. Instruction counter 2 is altered to reference the next instruction. Conditional branching instructions make it possible for a program to include intricate loops. A particular instruction can appear in each of several loops.

If a program error should appear during execution of such a much used instruction, identification of the error prehistory cannot normally be made.

The log of instruction addresses is controlled by program unit 6 which includes monitor mode switch 8. As a part of the standard operation during setup for execution of the instruction (during monitor mode), the content of instruction counter 2 passes via gate 9 to a recording device such as a tape unit. As soon as logging and other operations ar...