Browse Prior Art Database

IBM System/370 Other Equipment Manufacturers Information Bidirectional Bus

IP.com Disclosure Number: IPCOM000101939D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 141K

Publishing Venue

IBM

Related People

Moyer, JT: AUTHOR [+2]

Abstract

Original Equipment Manufacturers Information (OEMI) is the standard interface used to connect control units to all IBM System/360 and System/370 (S/370) computers. It uses two cables, each having 24 conductors. One cable carries the control lines that are referred to as TAGS IN and TAGS OUT. The other cable has the lines called BUS IN and BUS OUT, as well as two other lines called MARK O IN and MARK O OUT, hereafter referred to as MARK IN and MARK OUT. Communication is established between an interface channel and one of the 370 control units that are attached to it by placing the appropriate data on the appropriate bus and then raising the associated tag. This sequence is called initial selection and determines the direction for the flow of data.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 43% of the total text.

IBM System/370 Other Equipment Manufacturers Information Bidirectional Bus

       Original Equipment Manufacturers Information (OEMI) is
the standard interface used to connect control units to all IBM
System/360 and System/370 (S/370) computers.  It uses two cables,
each having 24 conductors.  One cable carries the control lines that
are referred to as TAGS IN and TAGS OUT. The other cable has the
lines called BUS IN and BUS OUT, as well as two other lines called
MARK O IN and MARK O OUT, hereafter referred to as MARK IN and MARK
OUT. Communication is established between an interface channel and
one of the 370 control units that are attached to it by placing the
appropriate data on the appropriate bus and then raising the
associated tag.  This sequence is called initial selection and
determines the direction for the flow of data. When the data transfer
begins, one set of bus lines becomes idle, either BUS IN for output
mode (write) or BUS OUT for input mode (read).  The data rate of the
channel can be doubled by defining the controls and adding additional
hardware to utilize the idle bus during data transfer, as described
in the following.

      Control units can coexist on the same interface with control
units that use a higher data rate.  This is done by using sequences
that are compatible with present control units.  Two new tag lines
are used; they are called ONE IN and ONE OUT and function in a
similar manner to SERVICE IN and SERVICE OUT.  The ONE IN and ONE OUT
tags also provide the means for data chaining, such as in the gaps of
direct access storage device (DASD) records, when a field has an odd
byte count.

      The hardware needed is a set of line drivers added to the bus
that previously only received data - BUS IN for the channel, BUS OUT
for the control unit, and a set of line receivers added to the bus
which previously had only drivers - BUS OUT for a channel, BUS IN for
a control unit.  This is to provide the capability for a two-byte
data transfer. Also, the ONE IN and ONE OUT lines must be equipped
with a line driver and a line receiver at each end.  ONE IN is driven
by the control unit and received by the channel; ONE OUT is driven by
the channel and received by the control unit.  Control units must
have a receiver for the MARK OUT line while channels must provide a
driver for the line.

      Information regarding the capacity of a channel or a control
unit to handle the two-byte transfer could be manually programmed
into the appropriate entities, but an optional automatic method of
signaling the capability of two-byte transfers is also described in
this article.  This signaling is done during the selection sequence.

      Control units signal TWO BYTE capability by raising MARK IN
when they place their address on BUS IN and then raising ADDRESS IN.
At STATUS IN time, MARK IN must be down or else TWO BYTE MODE will
be reset.

      If a control unit has signaled that it has TWO BYTE c...