Singer 40 - Write Operations Procedure; Writing Data to Sectors and Error Handling

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4 WRITE OPERATIONS
A Write instruction which addresses a disc drive causes 100 characters to be
accessed from memory and written onto a sector.
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If a Write instruction addresses a disc drive which is not on-line, the instruc-
tion is terminated and Condition Codes 4 and 1 (Fault) in the central processor
are set on.
When attached to the Disc Controller of a System Ten computer, the Models 40
and 42 Disc Drives automatically performed a "read after write" to check for
errors. After a record (100 characters) has been written, the next time the
sector passes the read/write heads the sector is read and compared against
the Write instruction's output area. If the content of the sector exactly matches
the content of the Write instruction's output area, the write operation is con-
sidered successful. If the operation is unsuccessful, writing (and reading) is
repeated up to two more times. If, after a total of three attempts, the write
operation still has not been successfully performed, the sector is marked ''bad,''
the operation is terminated, and Condition Code 3 (Flag) in the central processor
is set on.
If a Write instruction addresses a Model 42 Disc Drive and the requested
sector is one which would be accessed by the middle arm (arm 2), the instruc-
tion is terminated and Condition Code 3 (Flag) in the central processor is set
on.
If a FILE UNSAFE condition occurs during a write operation, the operation is
terminated and Condition Codes 4 and 1 (Fault) in the central processor are
set on.
NOTE: If the Disc Controller is addressed by a Write Control instruction,
the instruction is acted upon as though it were a Write instruction.
A write operation also records the track address on the particular sector. This track
address is used for track address verification during disc read operations.
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Models 40 and 42 Reference Manual 4-1