Difference between revisions of "AMSDOS Header"
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In [[AMSDOS]] it is possible to store files in two ways: headerless and with a header. Headerless files are often files which were created with [[OPENOUT]] and ''SAVE"filename",a''. Programs normally have a file header, which consist of 128 bytes and contain the following data: | In [[AMSDOS]] it is possible to store files in two ways: headerless and with a header. Headerless files are often files which were created with [[OPENOUT]] and ''SAVE"filename",a''. Programs normally have a file header, which consist of 128 bytes and contain the following data: | ||
| − | + | {| class="wikitable" | |
| − | + | |- | |
| − | + | ! Size !! Name !! Notes | |
| − | + | |- | |
| − | + | | BYTE || User number || 0-15, or #E5 for deleted entries | |
| − | + | |- | |
| − | + | | 8 BYTES || Filename || Unused characters are filled with space | |
| − | + | |- | |
| − | + | | 3 BYTES || Extension || Unused characters are filled with space | |
| − | + | |- | |
| − | + | | DWORD || Zero || Contains all zeroes | |
| − | + | |- | |
| − | + | | BYTE || Block number || Tape only | |
| + | |- | ||
| + | | BYTE || Last block || Tape only | ||
| + | |- | ||
| + | | BYTE || File type || 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers but a fake header is built in memory with the file type #16, "Unprotected ASCII v1") | ||
| + | |- | ||
| + | | WORD || Data location || Address of the 2KB buffer | ||
| + | |- | ||
| + | | WORD ||Load address || | ||
| + | |- | ||
| + | | BYTE || First block || Set to #FF, only used for output files | ||
| + | |- | ||
| + | | WORD ||style="white-space: nowrap;"| Logical length || Actual file length is here | ||
| + | |- | ||
| + | | WORD || Entry address || | ||
| + | |- | ||
| + | | 36 BYTES || Unused || | ||
| + | |- | ||
| + | | 3 BYTES || Real length || 24-bit number. Just a copy, not used! | ||
| + | |- | ||
| + | | WORD || Checksum || Unsigned sum of all bytes until this field | ||
| + | |- | ||
| + | |style="white-space: nowrap;"|59 BYTES || Unused || Free to use | ||
| + | |} | ||
To calculate the checksum just add all bytes from 00 up to and including byte 66 together. | To calculate the checksum just add all bytes from 00 up to and including byte 66 together. | ||
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This is only a summary. All details are in [[Firmware Guide]] chapter 9, page 4. | This is only a summary. All details are in [[Firmware Guide]] chapter 9, page 4. | ||
| − | [[Category: | + | [[Category:Disc Operating System]] |
| + | [[Category:Programming]] | ||
Revision as of 22:49, 12 January 2021
In AMSDOS it is possible to store files in two ways: headerless and with a header. Headerless files are often files which were created with OPENOUT and SAVE"filename",a. Programs normally have a file header, which consist of 128 bytes and contain the following data:
| Size | Name | Notes |
|---|---|---|
| BYTE | User number | 0-15, or #E5 for deleted entries |
| 8 BYTES | Filename | Unused characters are filled with space |
| 3 BYTES | Extension | Unused characters are filled with space |
| DWORD | Zero | Contains all zeroes |
| BYTE | Block number | Tape only |
| BYTE | Last block | Tape only |
| BYTE | File type | 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers but a fake header is built in memory with the file type #16, "Unprotected ASCII v1") |
| WORD | Data location | Address of the 2KB buffer |
| WORD | Load address | |
| BYTE | First block | Set to #FF, only used for output files |
| WORD | Logical length | Actual file length is here |
| WORD | Entry address | |
| 36 BYTES | Unused | |
| 3 BYTES | Real length | 24-bit number. Just a copy, not used! |
| WORD | Checksum | Unsigned sum of all bytes until this field |
| 59 BYTES | Unused | Free to use |
To calculate the checksum just add all bytes from 00 up to and including byte 66 together.
This is only a summary. All details are in Firmware Guide chapter 9, page 4.
