IBM Series 1 User Manual page 69
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- Quick installation manual (2 pages) ,
- User manual (114 pages) ,
- Manual (198 pages)
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Refer to Figure 2-20.
Each processor unit and I/O expansion
unit on the I/O channel has a self-contained power-on reset.
These
unit
power-on
resets are not electrically connected
among I/O or processor units.
For
example,
assume
that a system consists of a 4955
Processor Unit without the repower features and a
4959
I/O
Expansion
unit.
If
a
loss
of
pover
occurs on the I/O
expansion unit, outbound isolation is not provided.
The I/O
channel is inoperative and errors
may
occur.
When a channel repower feature is installed in a
unit,
the
feature
uses
the
power-on reset signal from the unit
immediately outbound of it to degate all
inbound
tags
and
busses
to
the
processor
whenever
the
outboard
unit is
powered down or actively generating a pover-on reset signal.
For example, if power went down on I/O expansion unit 2, the
power-on reset signal from unit 2 would be sent
across
the
cable
to the repower feature plugged in unit 1.
This would
cause the repower feature in unit 1 to
degate
any
inbound
signals from unit 2 and all other units outboard of unit 2.
The power-on reset of the unit containing
the
repower
card
is
used
only
to
initialize
certain latches on the
repower card;
outboard units are not directly
affected
by
this signal.
If I/O processing is taking place at the
time
of
the
loss of pover, an error may occur.
Indications of the error
are:
1.
2.
3.
4.
an
unexpected
condition
code
to
an
operate
I/O
instruction
an I/O interrupt with a condition code of 2 or 6
a machine check class interrupt with I/O check on
a machine check class interrupt with I/O check and
the
sequence indicator on.
The
error results from the fact that the processor may
continue to send outbound tags out,
but
inbound
tags
are
degated.
If
the
inbound tags are degated, this may cause
the channel to time out and cause the check.
An
indication
of
a
pover
loss
on the I/O channel is the reporting of a
condition code 000 to
Operate
I/O
instructions
that
are
directed
to
devices.
in
the
powered-down
card file or
outboard from the powered-down unit.
In
order
to
power the system up and down without I/O
checks, the following sequences must be observed:
2-54
GA34-0033
c
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