Techniques for applying modulation constraints to data using periodically changing symbol mappings

A method for imposing modulation constraints on data, the method comprising:

• extracting even-numbered bits from even-numbered symbols and odd-numbered bits from odd-numbered symbols in a data word to generate a data block;
• converting the data block from a first base into a first integer in a second base using a base conversion technique;
• substituting symbols in the first integer that match prohibited symbols with substitute symbols to generate a second integer;
• and
• interleaving bits in the second integer with odd-numbered bits from the even-numbered symbols and even-numbered bits from the odd-numbered symbols in the data word.

A disk drive system comprising:

• a disk drive controller chipset that includes a modulation encoder,
• wherein the modulation encoder extracts even-numbered bits from even-numbered symbols and odd-numbered bits from odd-numbered symbols in a data word to generate a data block,
• wherein the modulation encoder converts the data block from a first base into a first integer in a second base using a base conversion technique,
• wherein the modulation encoder substitutes symbols in the first integer that match prohibited symbols with substitute symbols to generate a second integer, and
• wherein the modulation encoder interleaves bits in the second integer with odd-numbered bits from the even-numbered symbols and even-numbered bits from the odd-numbered symbols in the data word to generate a constrained data word.