SAM Coupé file formats
The SAM Coupé exports one native binary — the .tap tape image SimCoupe and libspectrum read — plus a cassette .wav carrying the same tape as audio. Both round-trip back to editable source on import. Neither carries memory blocks, for a reason peculiar to this machine, described under the tape container below; blocks travel with the document through the project bundle and share links instead.
For the shared editor .txt, .zip project bundle, escape notation and the cross-machine machine-code overview, see the file formats overview. See also the SAM BASIC reference, its hardware notes and its escape codes.
SAM Coupé .tap
The blocks a real tape carries, each framed by a little-endian length word and then written out as it would be recorded: a type byte, the payload, and a parity byte that is the exclusive-or of everything before it, the type byte included.
The type byte is where the SAM parts company with the Spectrum whose pulse scheme it borrows:
| Type | Block |
|---|---|
0x01 | a SAM header |
0xFF | a data block |
0x00 | a Spectrum header, which the SAM ROM will also read |
One saved program is two blocks: a header and the data that follows it. A SAM header is 80 bytes, not the Spectrum's 17:
| Bytes | What they hold |
|---|---|
0 | File type: 16 program, 17 numeric array, 18 string array, 19 CODE, 20 SCREEN$ |
1–10 | The file name, padded with spaces |
11–14 | Four more name characters, for devices whose names run longer |
15 | Flags: bit 0 an invisible name, bit 1 protected code |
16–18 | Program length, excluding variables |
19–21 | Program length plus the numeric variables |
22–24 | Program length plus everything but the string and array variables |
25–30 | Directory entry and spares |
31–33 | Start address — ignored when a program is loaded, which always goes to PROG |
34–36 | Data length |
37–39 | Auto-run: 0xFF in the first byte for none, else a zero and the line number |
40–79 | A comment, which the ROM leaves uninitialised |
Every three-byte number above is in the ROM's page form: a 16 KB page number, then the two bytes of the address that page appears at in the 0x8000–0xBFFF window. The three length fields are what makes a load work — the loader deletes everything from the program area up to the edit line and rebuilds it to those three boundaries, so a header claiming no variable areas leaves a machine with none, and the first RUN or CLEAR afterwards walks off into memory that is no longer there. A freshly reset Coupé keeps 92 bytes in the first variable area and 512 in the second, which is why a program that never declares a variable still has areas to save.
The stored program ends in a 0xFF standing where a line number's high byte would be. It is part of the program area rather than a delimiter around it — the ROM's own line walk stops on it — so it is saved with the program and counted in every length the header carries.
Why no memory blocks. A SAM CODE file's header names its destination as a page number the ROM adds the saving machine's own low page register to, and the loader shifts it again by a page offset it keeps in a system variable. A CODE file's address is therefore only meaningful beside the paging it was written under, which an exported file cannot carry. The IDE's emulator writes a block into the processor's window directly instead, and the Transfer dialog asks before dropping blocks from an export that cannot hold them.
Disc images — .mgt, .sad and .dsk — are not read.
Cassette audio
The SAM exposes a .wav export (and "play through speakers") and a cassette-audio import — listening on the mic / line-in, or decoding a .wav recording, back into editable source. The encoder emits mono 44.1 kHz, and the audio carries exactly the blocks of the .tap above.
The scheme is the Spectrum's: a square wave whose level flips on every pulse, a long leader tone to lock onto, two short sync pulses, then two equal pulses per data bit — short for 0, twice as long for 1, most significant bit first.
The timing is not a round number, because the ROM makes it out of a delay loop rather than a table. The saver reads a speed register — DEVICE T<n> sets it, and the value the machine boots with is 112 — uses it as the short-pulse count L, derives the long-pulse count as 2 × (L + 1) + 1, and spends 13 × R + 33 T-states of a 6 MHz Z80 on a data pulse counted with R. That works out at 248 µs and 497 µs for the two data pulses, within 2% of the Spectrum's 244 µs and 489 µs — so a SAM tape written at the default speed plays back at very nearly Spectrum speed, rather than the 50% faster the machine's manual quotes for it. DEVICE T74 is the setting that gives the manual's 2250 baud.
Nothing downstream depends on the absolute figure. The ROM's loader locks onto the leader and measures every later pulse against its running average, which is why a SAM reads Spectrum tapes as happily as its own — and why the IDE's decoder recovers a tape written at any speed the machine can be set to.
On a real SAM Coupé, type LOAD "" — or press F7, which types it for you — and press ENTER before starting playback. To save, type SAVE "NAME" and press ENTER; the machine asks you to start the tape and press a key, and the tone then plays from the tape socket.