6-96
5. If no faults are found on the System ILPdata bus, the problem data line may be on the Waveform
ILPbus. Use the Waveform ILPKernel mode to check for faults while the busses are isolated.
4. Check that the data bus is at the "float" level during periods of inactivity (waiting for a response
from devices that are on the Waveform IlP bus). A HI or a LO in the idle period indicates a stuck
data bus.
3. Check that no data bus activity is occurring during the Waveform IlP address space (see Figure
6-10 to compare against). Faulty address decoding can cause response from an incorrectly
addressed device.
2. Recheck the faulty data bus line to determine if it is still faulty (problem on the System IlP data
bus) or the fault is gone (problem on the Waveform IlP data bus).
1. Move jumper J127 to the BUS ISOLATE position (pins 2 and 4 connected). This electrically
disconnects the Waveform IlP bus from the System ILP bus to isolate the different parts of the
processing system from each other.
BUS ISOLATE MODE
6. Check each of the System IlP data bus lines (07-00) on the outputs of Data Bus Buffer U650.
Look for open bus lines (no activity) and hung bus lines (stuck HI or LO). If a fault is found, it will
be necessary to determine if it is on the System Bus or the Waveform IlP bus. Use the BUS ISO-
LATE mode to assist in checking for a fault location.
NOTE
If the problem is that one of the selects is not being generated, the SELF TEST will be
able to determine that a group of registers fail. However, if two or more of the select
lines are shorted together, any addressed devices will try to respond at the same time
and bus contention will occur. The result is that the normal SELF TEST diagnostics
testing won't work.
5. With the power off, check that no two of the select outputs are shorted together. If shorted,
troubleshoot the cause and repair.
4. Check the host memory-mapped I/O selects at the outputs of U830 to verify that selects are gen-
erated and only during the time HMMIO is LO.
Table 6-6 (cont)
Maintenance-2430 Service
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