| 摘要 |
A method of modulation and demodulation of data converts data words of four bits to converted data words of twelve bits according to a normal coding scheme in which successive marks or "1" bits are separated by at least five spaces or "0" bits. At least two consecutive four-bit data words are furnished to a logic device that detects whether the last "1" bit of one converted data word corresponding thereto according to the normal coding scheme will be less than five bits from the first "1" bit in the next converted data word, and provides appropriate key bits; and converted data words are selectively provided according to the normal coding scheme and according to an alternate coding scheme in response to such key bits, so that in the modulated data, the "1" bits are always separated from each other by at least five "0" bits. For demodulation, a logic device provides a discrimination bit depending upon whether the converted data words have been modulated according to the normal or the alternate coding scheme, and a selector responsive to the discriminator bit selects data words according to the normal coding scheme and according to the alternate coding scheme. The apparatus for modulating data preferably includes an addressable ROM as a coding device. |
