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Binary-coded Decimals to Bit-significance Conversion

IP.com Disclosure Number: IPCOM000060626D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Fry, SM: AUTHOR [+2]

Abstract

In addressing peripheral devices, it is common to employ bit- significant indications in the peripheral subsystem. Binary- coded decimal input addresses have to be converted to the bit- significant indication. Enhanced performance in the conversion is achieved through using a bit mask and a truth table with checking for highly-reliable conversion.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 90% of the total text.

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Binary-coded Decimals to Bit-significance Conversion

In addressing peripheral devices, it is common to employ bit- significant indications in the peripheral subsystem. Binary- coded decimal input addresses have to be converted to the bit- significant indication. Enhanced performance in the conversion is achieved through using a bit mask and a truth table with checking for highly-reliable conversion.

The process includes firstly building a bit mask from the received binary- coded decimal (BCD). This mask is built by testing the received device address bit and logically ANDing the bits together to create a desired mask. For example, when the address "08" in hexadecimal is tested first to determine which half word of an address truth table the bit mask being created will be applied to. Then the "01" hex bit is tested and either a "55" hexadecimal (if the "01" bit is on) or an "AA" hexadecimal (if the "01" bit is off) is stored in a work or scratch register. Then the "02" hexadecimal bit of the received address is tested and the contents of the scratch register is then added with a "33" hexadecimal whenever the bit is on, or a "CC" hexadecimal when the bit is off. Then the "04" hexadecimal bit of the received address finally determines whether the scratch register is logically ANDed with "0F" hex when the "04" bit is on, or an "F0" hex when the "04" bit is off. The scratch register now has the mask corresponding to the received address for accessing a half word of th...