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Channel Attachment Circuit Employing a Single PLA

IP.com Disclosure Number: IPCOM000084390D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Reigel, FA: AUTHOR

Abstract

When a control unit or director is connected to a computer channel such as an IBM/360 or IBM/370 channel processor, certain channel signal sequences have to be decoded and interpreted for effecting selection and operation of the control unit by the channel. Previous interpretations of selection signals have been performed either in microcode by a micro-processor or by so-called random logic.

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Channel Attachment Circuit Employing a Single PLA

When a control unit or director is connected to a computer channel such as an IBM/360 or IBM/370 channel processor, certain channel signal sequences have to be decoded and interpreted for effecting selection and operation of the control unit by the channel.

Previous interpretations of selection signals have been performed either in microcode by a micro-processor or by so-called random logic.

Certain economies can be affected by using a single PLA (Programmable Logic Array) for performing all of the interconnecting interpretations and functions. The PLA has access to a small number of registers for storing intermediate selection results and status signals. An address decoder supplies driving signals to the PLA search array portion for being combined with output signals from a microprocessor in the control unit, and from a JK flip-flop register (REG) from the read or OR portion of the PLA.

Other outputs from the Read array portion control register access, and provide communications between the channel processor and data flow circuits of the control unit and with a device with its controller via a device attachment circuit.

The initial selection process has to be achieved in a predetermined minimal time. A minimal number of registers (Words) in the PLA (Search and Read portion), plus a high-speed addressing decoder, cooperate to select the search functions.

The Search array and Read array of the single chip PLA respo...