Browse Prior Art Database

State Machine for Scsi Bus Translation

IP.com Disclosure Number: IPCOM000099582D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 4 page(s) / 174K

Publishing Venue

IBM

Related People

Frazier, GR: AUTHOR

Abstract

A method is described which allows interconnections be- tween the differential version of the Small Computer System (SCSI) bus in which logic signals are carried by two wires such as "+sig" and "-sig" and the single-ended version of the bus where signals are carried by a single wire such as "-sig".

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This is the abbreviated version, containing approximately 49% of the total text.

State Machine for Scsi Bus Translation

       A method is described which allows interconnections be-
tween the differential version of the Small Computer System (SCSI)
bus in which logic signals are carried by two wires such as "+sig"
and "-sig" and the single-ended version of the bus where signals are
carried by a single wire such as "-sig".

      This is done by means of of a state machine and associated
resynchronization logic.  The logic states of the state machine
correspond to various interconnections between single ended and
differential devices.  This interconnection information is used by
resynchronization logic to insert the correct timing delays in the
bus signals and retransmit them.  Bus translators which simply
retransmit signals without regard to bus state information cannot
ensure that all SCSI bus timing relationships are met.

      INTERCONNECTION STATE DETECTION MACHINE There are six
interconnection states which this machine must detect.  These six
states are outlined below.
 D:  Differential device
 S:  Single-ended device
 STATE     INITIATOR      TARGET         CONNECTION TYPE
 I            S           D             Selection
 II           D           S             Reselection
 III          D           S             Selection
 IV           S           D             Reselection
 V            S           S             Selection or
 Selection
 VI           D           D             Selection or
 Reselection
                TABLE I

      States I - IV involve a connection between a single-ended and a
differential device in which the resynchronization logic synchronizes
and resends signals. States V and VI involve connections between two
single-ended or two differential devices.  For states V and VI, the
logic must  passively monitor the bus on which a connection has been
established (e.g., the single-ended bus for state V) and hold the
opposite bus (e.g., the differential bus) in the busy state until the
bus with the interconnection is freed.  The I/O diagram and signal
definitions of the interconnection state machine is shown in Fig. 1,
and the state diagram is shown in Fig. 2.

      This state machine uses SCSI arbitration level 7. Level 7,
which is the highest priority level, is used to ensure that whenever
an arbitration begins on one bus (e.g., single-ended bus), the
opposite bus (e.g., differential bus) is obtained.  After obtaining
the opposite bus by using level 7, however, the actual use of the bus
is transferred to the two levels which are actually connecting.  No
other single-ended or differential devices may use level 7.

      The operation of the state machine is seen by following the
progression of states which the machine goes through a...