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Browse Prior Art Database

Format for Serial Data Frame for Channel Extender Link

IP.com Disclosure Number: IPCOM000099572D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 126K

Publishing Venue

IBM

Related People

Brent, GA: AUTHOR [+3]

Abstract

A known serial channel extender has a bidirectional serial link and two boxes that connect one end of the link to the parallel bus of a data channel and the other end of the link to the parallel bus of a device control unit. The parallel bus has two sets of lines (bus in and bus out) for byte transfers and a set of parallel tag lines for controlling a transfer. For an output operation, the box connected to the channel processor forms a serial frame from the signals on the channel processor bus and transmits the frame over the link to the other box. The other box then puts the corresponding signals on the parallel bus to the control unit. An input operation on the channel extender is similar (*).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 48% of the total text.

Format for Serial Data Frame for Channel Extender Link

       A known serial channel extender has a bidirectional
serial link and two boxes that connect one end of the link to the
parallel bus of a data channel and the other end of the link to the
parallel bus of a device control unit.  The parallel bus has two sets
of lines (bus in and bus out) for byte transfers and a set of
parallel tag lines for controlling a transfer.  For an output
operation, the box connected to the channel processor forms a serial
frame from the signals on the channel processor bus and transmits the
frame over the link to the other box.  The other box then puts the
corresponding signals on the parallel bus to the control unit.  An
input operation on the channel extender is similar (*).

      In this channel extender, each frame is the same size and has a
command field, a one-byte data field, and a check bit field (a parity
bit or a multi-bit code).  As is conventional, a signal transition
represents a 0 bit, and the absence of a transition represents a 1
bit, and 0's are transmitted as idle bits to keep the clock circuits
synchronized.  The command field and the multi-bit check bit field
are arranged to contain 0 bits, and the longest sequence of all 1
bits (no clocking transition) is limited to the length of the data
field.

      The command field is only a few bits wide and the extender uses
three formats in which the same command codes have a different
significance.  Outbound frames (channel to control unit) have two
formats called control frames and data transfer frames, and inbound
frames have one format for both control and data transfer.

      The conventional I/O operation proceeds through three phases
called initial selection, data transfer, and ending sequence.
Outbound control frames are used during the initial selection and
ending sequence phases, and outbound data transfer frames are used
during the data transfer phase.

      For some of the messages that the channel processor and the
control unit exchange for initial selection and ending sequence, the
data field carries an address byte or a command byte or a status byte
that is also carried on the parallel bus and the command field
carries a code that identifies the accompanying tags.

      For other messages for initial selection and ending sequence,
the data field carries bits for the parallel bus tag lines and other
bits that control the transfer on the serial link.  These frames are
called tag frames.

      One bit in an outbound tag frame tells the control unit when
the frame format is being changed.  Other bits in this outbound tag
frame tell whether the forthcoming data transfer will be in an
interlocked mode or in a data streaming mode and, for data streaming
mode, the data transfer rate.  This information appears
conventionally on the parallel bus.

      The Wrap Frame:  When the box at the control unit end of the
link receives a tag frame with...