Browse Prior Art Database

Method of Handling Odd Byte Data Transfers On Small Computer System Interface Controllers

IP.com Disclosure Number: IPCOM000102734D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 61K

Publishing Venue

IBM

Related People

Keener, DS: AUTHOR [+2]

Abstract

A technique is described whereby odd byte data transfers, as used in small computer system interface (SCSI) controllers, eliminates problems associated with interrupts and disconnects occurring when an odd number of bytes are transferred.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 58% of the total text.

Method of Handling Odd Byte Data Transfers On Small Computer System Interface Controllers

      A technique is described whereby odd byte data transfers, as
used in small computer system interface (SCSI) controllers,
eliminates problems associated with interrupts and disconnects
occurring when an odd number of bytes are transferred.

      Originally, SCSI controllers were eight bit devices, such that
data from an attached SCSI device can be transferred to the local
system via an eight bit bus interface.  Subsequently, it was
determined that the bus width needed to be sixteen bits so as to
handle higher data rate and flow requirements of the controller.
Since this required the addition of a two byte data flow, problems
occurred with the management of odd bytes.  In addition, the SCSI
controller allows a target device to interrupt its data transfer and
a disconnect.  Disconnects are allowed to occur on any boundary.  If
a device transfers an odd number of bytes, then disconnects, it
eventually reconnects and attempts to continue the transfer.  The
concept described herein provides a solution for managing this
undesirable event.

      The technique used to solve the problem first identifies which
of the bytes of data presented are valid. This is accomplished by
initiating two signals called "High Byte Valid" and "Low Byte Valid".
These signals tell the data controller if the byte of data is to be
transferred. The data controller uses these signals for error
...