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IBM 1 Series - Page 66

IBM 1 Series
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Unit-Load
Characteristics
This
section
describes
the
specifications
for
a
unit
load
on
the
channel.
A
device
adapter
or
attachment
represents
a
single
drop
on
the
I/O
channel.
It
can
represent
one
or
more
logical
devices,
each
with
a
device
address.
For
a
device
adapter
to
attach
to
the
I/O
channel
and
not
restrict
the
I/O
configuration
because
of
improper
loading,
it
must
present
a
unit
load
to
the
I/O
channel.
A
unit
load
means
that
every
specification
on
each
of
the
drivers
and
receivers
to
each
I/O
channel
line
has
been
met
or
exceeded.
A
violation
of
any
of the
driver/receiver
specifications
constitutes
a
violation
of
the unit-load
requirement.
Proper
operation
of
the
channel
under
these
circumstances
would
then
be
dependent
on
the
particular
configuration
of
attachments
on
the
channel
and,
consequently,
would
be
generally
unpredictable.
Figure
2-24
shows
the
classifications
of
driver/receiver
types
to
I/O
channel
signal
lines.
Figure
2-25
illustrates
each
driver/receiver
type
in
general
terms
and
establishes
the
reference
current
direction
for
the
elements
of
each
type.
Figure
2-26
shows
the
drivers
and
receivers
for
each
type.
Two
types
of
unit
loads
are
specified:
a
general
unit
load
and
a
TTL
unit
load.
IBM
attachments
present
general
unit
loads
to
the
interface.
Processor
I/O
Channel
2-55

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