Z80to

Simple utility to convert Sinclair ZX Spectrum Z80 or SNA snapshots to tape, cartridge or disk format so they can be loaded on real hardware with the appropriate device. Works with Tape, Sinclair Microdrive, Opus Discovery, MGT Plus D, TR-DOS and +3 Disks. It supports either 48k or 128k snapshots.

The utility eliminates screen corruption, which a lot of the other conversion tools suffer from, by using compression and a custom 4 stage launcher. Once memory is restored the only difference between this and the original snapshot will be a few bytes under the stack.

This brings all my Z80on utilities into one code base, ensuring any updates are now made across all formats. As per the other utilties you can either create a single snapshot per tape/cartridge/disk or one with multiple snapshots included and a menu to load them. You can also replace the loading screen with a custom one, as long as there is space.

I've also made some further advancements in this version such as ability to autodetect 48k snapshots incorrectly saved as 128k and the ability to not store blank 128k memory pages to save space. The menu and loader codes are now all in BASIC and unified across all formats, apart from the LOAD commands which have to differ.

I originally created this utility to accompany my ZXPicoMD device (https://github.com/TomDDG/ZXPicoMD) as very few Microdrive cartridges where released in the 1980s.

I highly recommend using Skoolkit (https://skoolkit.ca/skoolkit/) to create "perfect" snapshots to use with this utility. Skoolkit will create the snapshot as soon as the game has loaded which has the advantage, in most cases, of removing the need to add a loading screen back in.

Z80to v1.4 ©Tom Dalby 2025
Usage: z80to [Output Format] <Global Options> "InputFile" <InputFile Options>

Output Format:
  -t               Create Cassette [.TAP] Tape Output
  -m               Create Microdrive [.MDR] Cartridge Output
  -o               Create Opus Discovery [.OPD] Disk Output (SSSD)
  -q               Create Opus Discovery Quick DOS [.OPD] Disk Output (DSDD)
  -p               Create Plus D [.MGT] Disk Output (DSDD)
  -d               Create +3DOS [.DSK] Disk Output (SSSD)
  -r               Create TR-DOS Disk [.TRD] Output (SSDD)

<Global Options>
  -n "Name"        Add menu, titled "Name" (max 10chars). Min 2, max 16 snapshots
  -c               Create TAP copy of disk, used for transfer

"InputFile"        .Z80 or .SNA snapshot. 48k & 128k supported

<InputFile Options>
  -l screen.scr    Use Alternate Loading Screen (must by 6912byte SCR)
  -f               Force 48k removing any 128k memory banks & disabling paging
  -k               Keep 128k fully intact (-f overrides)

Examples:
  z80to -m mminer.z80
    Creates Microdrive Cartridge with single snapshot
  z80to -o mminer.z80 jsw.z80
    Creates OPD disk with two snapshots
  z80to -p -n "MM+JSW" mminer.z80 jsw.z80 -l jsw.scr
    Creates MGT disk with two snapshots & menu titled "MM+JSW". jsw has an alternate loading screen
  z80to -r -c mminer.z80
    Creates TR-DOS Disk with single snapshot and a TAP copy for transfer

Versions

• v1.0 - initial release
• v1.0a - fixed 3DOS naming convention
• v1.1 - 3DOS now works with 128k snapshots
• v1.2 - TR-DOS disks format added (SSDD only)
• v1.3 - Added Quick DOS DSDD disk support for Opus Discovery
• v1.4 - Added TAP copy option

4 Stage Launcher

Restoring ZX Spectrum's full memory and registers without the aid of an external device requires the launch code to reside within the memory you are trying to restore and this is why the screen is often used. The screen is usually a "safe" place as execution code is not normally placed there, although there are some exceptions. The issue with using the screen is it causes corruption which looks a mess which isn't always cleared after loading. Ideally we wouldn't use it, but in order to do that we need to find somewhere else to put the launcher code. Options are:

• Immediately under the stack as this space is usualy intentionally free as it is requied for the main code, although there is no indication on the size available and some code does use the stack for more than register storage. If the snapshot is immediately after load then use of the stack is most likely to be for storage.
• A gap within the main code, usually a block of 0x00, which may or may not be used. As there is no way to tell if it is used then restoring after use is recommended.
• The printer buffer immediately after the screen, although this may be used by the program. As there is no way to tell if it is used then restoring after use is recommended.

Ultimately to have the best compatibility we need to use a combination of all of the above, which is how the 4 stage launcher works.

3DOS

Getting 128k snapshots to work on a +3 was a challenge. Unlike the other formats 3DOS makes extensive use of memory bank 7, even after disabling the RAM drive and disk cache. As a result, and if a snapshot contains data in bank 7, the launcher becomes a lot more complicated. This is why the original release of this utility only supported 48k snapshots as these don't require restoration of bank 7.

In my original Z80onDSK utility I simply used the screen for the launcher and storing bank 7, but this causes a lot of corruption which looks a mess. As this is a unified utility I wanted 3DOS to match the others with zero corruption unless absolutely necessary. In order to do this I had to split bank 7 into 2 parts. Part 1 contains the memory areas around the area 3DOS uses, and this is loaded as per the other memory banks. The 2nd part is then added to the main compression and decompressed only after 3DOS has finished. This is the only time it is safe to overwrite the 3DOS area of bank 7. If there isn't enough room, then the screen is used as the last resort.

The only other change from the other formats is the handling of the alternate loading screens. For the other formats these are added to the main compression if there is enough memory. If there isn't enough memory then the final screen is loaded at the end, basically as a normal SCREEN$. Due to the bank 7 decompression 3DOS always puts the final screen at the end and never in the main compression.

Motor timeout

On a +3 machine running 3DOS the 48k ROM contains an additional motor timeout routine which will run on an interrupt. This ROM routine uses memory location 0xe600 in bank 7 and over time will decrease the value held at this location to zero, upon which the motor is switched off. If the snapshot requires this memory location to be anything other than zero and the standard ROM interrupt is on then it may not work as the ROM routine will continually decrease this value on each interrupt.

TR-DOS

BASIC loader needs to be called behind a RANDOMIZE USR and REM statements.

RANDOMIZE USR 15619: REM: LOAD "program"