Diagnostic Aids; Control Panel Leds; Line Sync; Line Check - IBM 5251 Series Maintenance Information Manual

Diagnostic Aids
200
CONTROL PANEL LEOs
The following five lights (LEDs) are located on the
control panel of the display station: Line Sync, Line
Check, Internal Check, Storage Check, and Ready.
These lights are used by the operator and the customer
engineer. All five lights are on briefly during power on
to test the LEDs. After power on, use the following
descriptions.
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 there are more than 160 ms between
recognized characters.
Line Check
When on, this light indicates that the display station has
sensed a parity error in the poll or data that 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 particular work
station. The addressed work station returns an error
response to the controller. The controller resends the
information that caused the error until the display station
receives the information without any errors; at this time,
the light turns off.
Internal Check
When on, this light indicates that a parity error has been
found in the data bus while the display station is getting
data from read/write storage. You can reset the Internal
Check light 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)
1-104
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 M PU controls this light.