Difference between revisions of "AMSDOS Header"
From CPCWiki - THE Amstrad CPC encyclopedia!
PulkoMandy (Talk | contribs) m |
|||
| (6 intermediate revisions by 3 users not shown) | |||
| Line 1: | Line 1: | ||
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" | |
| − | + | |- | |
| − | + | ! Offset !! Size !! Name !! Notes | |
| − | + | |- | |
| − | + | | 0 || BYTE || User number || 0-15, or #E5 for deleted entries | |
| − | + | |- | |
| − | + | | 1 || 8 BYTES || Filename || Unused characters are filled with space | |
| − | + | |- | |
| − | + | | 9 || 3 BYTES || Extension || Unused characters are filled with space | |
| − | + | |- | |
| − | + | | C || DWORD || Zero || Contains all zeroes | |
| − | + | |- | |
| − | + | | 10 || BYTE || Block number || Tape only | |
| + | |- | ||
| + | | 11 || BYTE || Last block || Tape only | ||
| + | |- | ||
| + | | 12 || 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") | ||
| + | |- | ||
| + | | 13 || WORD || Data location || Address of the 2KB buffer | ||
| + | |- | ||
| + | | 15 || WORD ||Load address || | ||
| + | |- | ||
| + | | 17 || BYTE || First block || Set to #FF, only used for output files | ||
| + | |- | ||
| + | | 18 || WORD ||style="white-space: nowrap;"| Logical length || Actual file length is here | ||
| + | |- | ||
| + | | 1A || WORD || Entry address || | ||
| + | |- | ||
| + | | 1C || 36 BYTES || Unused || | ||
| + | |- | ||
| + | | 40 || 3 BYTES || Real length || 24-bit number. Just a copy, not used! | ||
| + | |- | ||
| + | | 43 || WORD || Checksum || Unsigned sum of all bytes until this field | ||
| + | |- | ||
| + | | 45 || 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. | ||
| Line 19: | Line 42: | ||
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]] | ||
Latest revision as of 15:49, 7 November 2023
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:
| Offset | Size | Name | Notes |
|---|---|---|---|
| 0 | BYTE | User number | 0-15, or #E5 for deleted entries |
| 1 | 8 BYTES | Filename | Unused characters are filled with space |
| 9 | 3 BYTES | Extension | Unused characters are filled with space |
| C | DWORD | Zero | Contains all zeroes |
| 10 | BYTE | Block number | Tape only |
| 11 | BYTE | Last block | Tape only |
| 12 | 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") |
| 13 | WORD | Data location | Address of the 2KB buffer |
| 15 | WORD | Load address | |
| 17 | BYTE | First block | Set to #FF, only used for output files |
| 18 | WORD | Logical length | Actual file length is here |
| 1A | WORD | Entry address | |
| 1C | 36 BYTES | Unused | |
| 40 | 3 BYTES | Real length | 24-bit number. Just a copy, not used! |
| 43 | WORD | Checksum | Unsigned sum of all bytes until this field |
| 45 | 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.
