NEX file format
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Revision as of 07:03, 31 March 2019 by wiki>Ped7g
The NEX file format was designed as very simple and straightforward format to load self-contained applications into memory and start them. Through various extensions it did reach v1.2 at this moment, which allows even for more complex use cases.
The basic structure of the file is:
| block size | optional | description |
|---|---|---|
| 512 | "Next" string followed by file header, containing also map of memory banks stored in the file | |
| 512 | * | optional palette (for Layer2 or LoRes screen) |
| 49152 | * | Layer2 loading screen |
| 6912 | * | classic ULA loading screen |
| 12288 | * | LoRes loading screen |
| 12288 | * | Timex HiRes (512x192) loading screen |
| 12288 | * | Timex HiCol (8x1) loading screen |
| n * 16384 | * | 16kiB raw memory bank data in predefined order: 5,2,0,1,3,4,6,7,8,9,10,...,111 (particular bank may be omitted completely) |
Structure of the header block: The basic structure of the file is:
| offset | size | description |
|---|---|---|
| 0 | 4 | "Next" string |
| 4 | 4 | string with NEX file version, currently either "V1.1" or "V1.2" |
| 8 | 1 | RAM required: 0 = 768k, 1 = 1792k |
| 9 | 1 | Number of 16k Banks to Load: 0-112 |
| 10 | 1 | Loading-screen blocks in file (bit-flags):
128 = no palette block, 16 = Hi-Colour, 8 = Hi-Res, 4 = Lo-Res, 2 = ULA, 1 = Layer2 |
| 11 | 1 | Border Colour: 0-7 |
| 12 | 2 | Stack pointer |
| 14 | 2 | Program counter (0 = don't run, just load) |
| 16 | 2 | "Number of extra files" (currently not used by anything/anyone?) |
| ... work in progress ... |