Browse Prior Art Database

Serial Channel to I/O Interface

IP.com Disclosure Number: IPCOM000087409D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 90K

Publishing Venue

IBM

Related People

Lynch, KR: AUTHOR [+2]

Abstract

This publication describes a mechanism which can be used to replace all or part of a parallel I/O interface (such as used on an IBM System/36O or System/37O) with a serial I/O interface without changing any channels or control units.

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Serial Channel to I/O Interface

This publication describes a mechanism which can be used to replace all or part of a parallel I/O interface (such as used on an IBM System/36O or System/37O) with a serial I/O interface without changing any channels or control units.

Referring to Fig. 1, the mechanism uses two boxes, "OUT" and "IN", that are interconnected by means of two links over which serialized information is transferred. The "OUT" box is connected on the end of the serial link closest to the channel, while the "IN" box is connected on the control unit end.

The "OUT" box serializes the "out" tags and "out" bus lines and transmits them on one link, while deserializing any information received on the other link and placing it on the "in" tag and "in" bus lines. The "IN" box serializes the "in" tags and "in" bus lines and transmits them on one link, while deserializing any information received on the other link and placing it on the "out" tag and "out" bus lines. Each box is thus divided into two sections, one for serializing and one for deserializing information.

On each link, infonmation flows in only one direction. The information flow on one link is opposite the direction of information flow on the other link. The serialized information is transferred over the link in packets called frames. A frame is composed of a unique means of identifying the beginning of the frame, called a flag, followed by the serialized information. The technology of the link can be anything that is of sufficient speed to handle the data rate required by the device or devices attached to the interface.

General Operation. The two serial links are constantly active. Each serializer is continually sending complete frames or transmitting flags only, and the two deserializers are constantly monitoring their respective links for frames and flags. The serializers transmit a frame whenever transitions are detected on certain lines of the parallel interface. At all other times, the serializer sends flags only. There are two possible flags, "normal" or "error". The deserializer in each box continually conditions the serializer in that box as to which flag is to be sent. As long as the deserializer receives frames with good parity, it causes its serializer to continue generating normal flags. Whenever the deserializer receives a frame with bad parity, it causes the serializer to generate error flags until the deserializer receives a frame with correct parity.

Whenever the deserializer receives an "error" flag, it causes the serializer to resend the last frame. The deserializer causes the serializer to repeatedly resend the last frame until the deserializer receives a "normal" flag. The scheme improves the RAS (reliability, availability, serviceability) characteristics of the I/O interface by detecting parity errors occurring on the frames which include both bus and tag information. When an error is detected, simple and automatic predefined procedures cause the re...