Honeywell BR3C9 Operation Manual page 150

1. Controller issues Set Diagnostic Escape.
2. Controller issues Write Test command.
This enables the normal write circuitry.
The normal Serial Read In/Serial Write
Out dialog explained in Write Operations
begins.
3. Controller writes a selected number of
bytes with a
10101~10
pattern.
a. Data is processed by SERDES as it
does during a normal Write command.
As the NRZ data leaves SERDES, the
bit toggling is checked by one-shot
A676. It must receive a "1" at least
once each 800 nanoseconds. Since
the data pattern (10101010) normally
creates toggles, SERDES is malfunc-
tioning if the one-shot times out.
This sets Not NRZ Toggle FF which,
in turn, sets the NRZ Fault FF.
See step 5.
83318200 A
4. Controller raises Data Modifier Line to
inhibit MPH clock/data writing.
a. Fault Inhibit A and Fault Inhibit B
flip-flops set. They inhibit Current
Fault FF (DS2 bit 25) as they do dur-
ing regular address mark operations.
b. Lack of write driver transitions
generates a Current Fault. Although
the CUrrent Fault FF is inhibited,
the fault is still indicated inter-
nally. If the fault is not generated
(hardware error), Write TeSt Current
Fault FF sets.
5. Controller drops Write Test and raises
Write Test Check.
a. If NRZ Fault (error condition)
occur~
red in step 5, bit 20 of the bidirec-
tional data lines is true.
b. If a Current Fault did not occur in
step 4, bit 21 of the bidirectional
data lines is true.
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