NEC D765AC-2
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NEC D765AC-2 supports FM and MFM recording.
MFM
Some FDCs are quite relaxed in the data that they accept. The following applies to the NEC D765AC-2 and was found through testing:
- The only address mark which identifies the ID field is 0x0fe. Attempting to use any other mark for an ID field will result in the ID field being ignored.
- The only data marks which identify the data field are 0x0fb (Data) and 0x0f8 (Deleted Data). Attempting to use any other mark fo a data field will result in the field being ignored.
- Only 3 sync marks (4489) can proceed an ID field or data field. Fewer or more are ignored.
- When a valid ID field has been read, the data field must be found within a certain number of bytes from the end of the ID field. The minimum is 33 bytes. The maximum is around 44 but needs to be determined.
- Sector within sector is possible.
- If an ID field with a CRC error is found then the data field will not be read when using Read Data or similar commands.
- Any data can exist in Gap 2 and will not affect reading of the ID fields or sectors.
- Any data can exist in Gap 3 and will not affect reading of the ID fields or sectors.
