Browse Prior Art Database

Host Interface Communications and Control Unit Emulation

IP.com Disclosure Number: IPCOM000084155D
Original Publication Date: 1975-Sep-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 26K

Publishing Venue

IBM

Related People

Loughlin, MP: AUTHOR [+2]

Abstract

This is a software controlled interface external to the Central Processing Unit (CPU) and software of a major operating system, which is capable of providing control unit emulation to interface devices with the large system.

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Host Interface Communications and Control Unit Emulation

This is a software controlled interface external to the Central Processing Unit (CPU) and software of a major operating system, which is capable of providing control unit emulation to interface devices with the large system.

A combination of a small CPU, such as an IBM System/7, with channel termination hardware and a portion of the control program in the small CPU provide an interface, which appears to the channel and CPU for a large system such as an IBM System/360 or System/370, to be a device control unit. In the current implementation, the control unit which is emulated is one which handles telecommunication devices. However, with suitable software modifications any type of control unit may be emulated on multiplex, selector or block multiplex channels.

The channel termination hardware (CA) contributes: address recognition to provide interrupts to the software when the control unit or device related to the control unit is addressed, automatic busy response when the software fails to respond within a given time limit, and adherence to the normal polling protocol required during command, command response and information exchange. The CA gives two levels of interrupts: one for initial selection, a high-priority interrupt, and a low-priority interrupt for subsequent command handling, and data or status movement.

The software portion of the emulator is called the Data Handler Communication routines (DHC). The DHC series as an interface between the major or host CPU 4 and channel and the remainder of the control program in the small CPU 2 (emulator). The operation of the DHC is table driven, which is based on the previous status of the device and the current status.

The emulation includes standalone operation which allows user connection before CPU and function of major system utilizes lines, stays up through major system failures and reset, and commands recognized beyond basic support command set can be extended or replaced to yield new control unit emulators.

The DHC routines with the use of the CA on a small CPU 2 provides the capability of attaching the small CPU to a System/360 or a System/370 computer 4 via a standard byte multiplexer 6 I/O interface for controlling a terminal device
8. The DHC, within the control program, receives interruptions for each host selection, and at the end of each data burst or status transfer. The data and status transfers are storage-to-storage between the control unit emulating CPU and host.

For a host selection or initial selection the interrupt is a high-priority interrupt. For this in...