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Byte 1
Bits 7, 6
00 - Normal termination
01 - Abnormal termination (This is a normal termination, in this system)
10 - Invalid command
11 - Abnormal due to polling
Bit 5
Seek or Recalibrate complete
Bit 4
Track-0 signal not found
Bit 3
Unused
Bit 2
Selected side
Bits 1, 0
Selected drive
Byte 2
Bit 7
Did not see TC at end of sector (This is normal, in this system)
Bit 6
Unused
Bit 5
CRC error
Bit 4
DMA under/overrun
Bit 3
Unused
Bit 2
No data seen
Bit 1
Write Protect
Bit 0
Missing address mark
6.4
An Example
One board worked on everything except booting the system. Running the above
disk test gave a "DMA underrun" error. A continuity checker showed a missed
joint at the DMA request input to the CPU. Voil` a !
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