Data - an encoder with read - advance compensation and mfm algorithm and a process for the corresponding signal shaping

摘要

An encoding circuit for converting an input stream of serial data bits at (12) to an MFM encoded output stream of serial data bits with write precompensation comprises a ROM (4) acting as a look-up table and providing an MFM coding for a current bit at QB the coding depending upon the previous two bits at QC, Q1, as well as the next, at Qa, the encoded signal being provided in serial format 22. With write precompensation, a transition which would be expected at either of the positions "NORMAL" Fig. 2 is shifted to +/-250 nS in dependence on the ROM algorithm. The precompensation corrects for bit shifting which otherwise occurs when MFM data is recorded on the inner tracks of a magnetic disc recorder. The presence or absence of precompensation is controlled by a signal at A4. Use of delay lines for precompensation is thus avoided. IMAGE