During this phase, the actual data is transferred (if any). Usually that are the data bytes for the read/written sector(s), except for the Format Track Command, in that case 4 bytes for each sector are transferred.
During data transfers between the FDC and the processor, the FDC must be serviced every 26us 26µs (for MFM mode with CPC timings) or the FDC terminates the FDC command.
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