Diagnostic Aids - IBM 5251 11 Maintenance Information Manual

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Diagnostic Aids
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CONTROL PANEL LEOs
Five lights (LEDs) are located on the control panel of the
display station, and are used by the operator and the
customer engineer. All five lights are on momentarily
during power on to test the LEDs. After power on, the
following descriptions apply. The lights are:
Line Sync: When on, this light indicates that the
display station has recognized a poll or data that the
controller sent over the system cable. The poll or data
can be for any display station on the cable (Cable Thru
feature). The light goes off if more than 160 ms elapse
between recognizable characters.
Line Check:
When on, this light indicates that the
display station has detected a parity error in the poll or
data the controller sent. When the Cable Thru feature is
installed, each display station turns this light on even if
the poll or data is not addressed to that work station.
The addressed work station returns an error response to
the controller. The controller resends the information
that caused the error until the information is received at
the display station error free, at which time, the light will
be turned off.
Internal Check:
When on, this light indicates that a
parity error has been found in the data bus while getting
data from read/write storage. The Internal Check light
can be reset (off) by setting the Test switch to the Test
position. A power on reset occurs when this light is
being reset by the Status switch.
Storage Check: (reserved)
Ready:
When on, this light indicates that the power-on
diagnostic has completed correctly. The Ready light is
off if the Status switch is in the Test position; if either
or both the Storage Check and Internal Check lights are
on; or if the microprocessor is in a diagnostic sequence.
The MPU controls this light.
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Maintenance Procedures 5251 MIM 1-59