Tandberg Data
Track, Tape format and Encoding Specification
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Tandberg SLR Reference Manual
6-9
1. PHASE
The phase metric is a decimal value with a range 0 to 127. The phase metric is initialized at
the end of a preamble with a value of decimal 20. The phase metric is updated, following the
processing of each incoming bit.
If the value of new phase is less than or equal to decimal 13 then a single bit is inserted as
explained in VR
2
RLL coding, Section 6.4.2.1.
2. NULL
The null constraint limits the number of consecutive '0's to eight. The null metric
, N,
can be
considered as a counter with range 0 to 15 that is either incremented or reset to 0 following
the processing of each incoming bit.
N
is initialized to 1 at the end of a preamble.
If
N
is greater than or equal to 8 then a single bit is inserted as explained in VR
2
RLL coding,
Section 6.4.2.1.
3. AMPLITUDE
The amplitude constraint ensures adequate amplitude content in the encoded data. The
amplitude metric,
A
, can be considered as a counter with a range 0 to 63 that is either
incremented or reset to 0 following the processing of each bit.
A
is initialized to 2 at the end of
a preamble.
If
A
is greater than or equal to 60 then a single bit is inserted as explained in VR
2
RLL coding,
Section 6.4.2.1.
4. PREAMBLE PATTERN
The preamble pattern constraint inhibits a preamble pattern from occurring in a field other
than in the preamble itself. The preamble metric,
P
, can be considered as a counter with a
range 0 to 15 that is either incremented or reset to 0 following the processing of each bit.
P
is
initialized to 0 at the end of a preamble.
If
P
is greater than 10 then a single bit is inserted as explained in VR
2
RLL coding, Section
6.4.2.1.
6.4.3. Data Encoding; GCR 0,2 Rules
The GCR 0,2 rules are used for the QIC-2GB and QIC-4GB tape formats.
The GCR 0,2 rules are described in the Tandberg SLR (TDC 4000) Series Reference Man-
ual.