Browse Prior Art Database

Eight Bit Loader for Preconditioning Programs

IP.com Disclosure Number: IPCOM000090930D
Original Publication Date: 1969-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Bishop, DA: AUTHOR [+2]

Abstract

The table shows a technique of modifying the contents of bytes subsequent to reading them to provide a modified byte content which, if originally read, would be prohibited or cause undesirable systems response. Often a system has a wired-in response to bits in certain positions of a byte such that, when the bit is read, an automatic response occurs. While this approach facilitates control, it severely limits the system in that, during program load, these bit positions cannot be used either for addressing or data storage purposes.

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Eight Bit Loader for Preconditioning Programs

The table shows a technique of modifying the contents of bytes subsequent to reading them to provide a modified byte content which, if originally read, would be prohibited or cause undesirable systems response. Often a system has a wired-in response to bits in certain positions of a byte such that, when the bit is read, an automatic response occurs. While this approach facilitates control, it severely limits the system in that, during program load, these bit positions cannot be used either for addressing or data storage purposes.

In the example shown, any 1 in bit position BP 8 is not allowed and only bit positions 1...7 are used. To provide bit 8, an address steering character ASC and a byte steering character BSC are used. At word time 1, the ASC is read and stored. At word time 2, the high-order address byte is read and the 1 bit from BP 7 of the ASC is used to change the 0 bit in BP 8 of the byte to 1 prior to entry into the memory address register. Similarly, the 1 bit from BP 6 of the ASC is used to change the 0 bit of BP 8 of the low-order address bit to 1.

The BSC is then read and the bits contained in it are used to change BP 8 of bytes 1...7 in like manner.

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