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ZX Interface 1: Difference between revisions
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→Microdrive Data Storage Format
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Each sector consists of two files, each similar. There is the Sector Header, which is a 15 byte file record, or the data record recorded after the sector header, which is 528 bytes, including one "sacrificial byte" on the D1 data line, which does not contribute to the data stored, though could be modified into a high-order byte checksum in the future to improve data integrity on older cartridges. | Each sector consists of two files, each similar. There is the Sector Header, which is a 15 byte file record, or the data record recorded after the sector header, which is 528 bytes, including one "sacrificial byte" on the D1 data line, which does not contribute to the data stored, though could be modified into a high-order byte checksum in the future to improve data integrity on older cartridges. | ||
All bytes are written LSB ( Least Significant Bit ) first. | All bytes are written LSB ( Least Significant Bit ) first. Here's how to read the images, as data is spread across two data lines. | ||
[[File:How to read the decodes.png]] | |||
=== Sector, including header and data === | |||
As the spectrum uses soft-coded sectors, without any indication of tape start and end, each Microdrive cartridge is a collection of sectors that present sequentially to the reader and are read at random, depending on where the loop happens to be when a particular read operation occurs. The sectors do not require to be in order, or to follow any convention. Typical sectors are sequential in nature, however interleave to allow time for internal transfer between reading and writing sectors seems to be accomplished through the process, such that any new writes rarely write in two physically consecutive sectors. The sector format includes a header and a record. The header is only written during the format operation, while the record can be written at any time it is unused. Bit 2 in the RECFLAG byte, the first byte of the sector, identifies whether it is in used. If set, it is used. If unset, it is not used. | |||
[[File:Logic_Analysis_of_sector_Header_and_Data_sections_with_gaps.png]] | [[File:Logic_Analysis_of_sector_Header_and_Data_sections_with_gaps.png]] | ||