Thomson MO5 Emulation in MESS

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Thomson MO5 (French, Jun 1984)

Driver name: mo5

The MO5 is Thomson's attempt to provide a low-cost version of the TO7/70.

It is based on the same gate-array technology, but has less memory and is less expandable. Please note that it is software incompatible with the TO7 and TO7/70.





An optional .m5 or .rom cartridge can be used (-cart option). Note that, unlike the TO7 and TO7/70, the MO5 is usable without a cartridge as the BASIC 1.0 is already included in ROM.

Due to major system incompatibilities, TO7 and TO7/70 cartridges cannot be run on a MO5.


Most games were distributed on cassettes.

They are used in the same way as for the TO7. You must insert them with the -cass option, and then either type RUN"" (for BASIC programs or loaders) or LOADM"",,R (for binary code programs) at the BASIC prompt. Using the wrong option will get you an error, so, you should try both.

Cassette images can be raw sound files (.wav) or demodulates byte streams (.k5 or .k7).

Cassettes are slow, be patient (or put off throttling).

See the to7 driver for more information.

the cassette encoding is different and incompatible with that of the TO7, TO7/70. You cannot read TO7 .wav or .k7 files on a MO5.

For the MO5 format, the .wav format is more robust than .k5 and .k7 and will work better.

Cassettes are always saved in .wav format.


Floppies are used in the same way as for the TO7.

Here is a quick checklist (see the to7 driver for more information):

MO5 floppy format and floppy images (.sap, .qd, .fd) are fully compatible with the TO7 ones. You can easily read TO7 floppies and load TO7 files on a MO5.

However, due to major system incompatibilities, TO7 programs will not be runnable (except pure BASIC programs).


It is similar to the TO7 one:

  STOP  1!  2"  3#  4$  5%  6&  7'  8(  9)  0  -=  +;  ACC      UP  DOWN

  CTRL    A   Z   E   R   T   Y   U   I   O   P  /?  *:        LEFT RIGHT

  RAZ       Q   S   D   F   G   H   J   K   L    M   ENTER        TOP

  SHIFT       W   X   C   V   B   N   ,<  .>  @^     BASIC      INS DEL


As in the TO7/70, accented keys are typeset using the ACC key, and CAPS-LOCK is toggled with the SHIFT+SPACE combination.

The only differences are:

Known Issues

History and Trivia

The MO5 is the first Thomson computer with an integrated BASIC. Unlike the TO7 and TO7/70, it does not require an external BASIC cartridge to operate.

Also, the MO5 (and its MO5E variant) is the only Thomson computer without a startup menu: it starts directly at the BASIC prompt (or whatever cartridge was plugged-in).

This is also the first Thomson computer of the so-called MO family (that also spawned the MO6, MO5NR and Olivetti Prodest computers) which is incompatible with the TO family (TO7, TO7/70, and later TO8, TO9, TO9+) despite being based on similar hardware. Causes of incompatibility are numerous. The address map is different. The calling conventions to BIOS functions are different. The Motorola 6846 programmable timer is missing (replaced with a fixed clock). The encoding of colors is incompatible (albeit more reasonable than the TO7/70 one that strives for TO7 compatibility). The cassette encoding is completely different (albeit more effective, robust, and simpler to implement). The reason for all this is not very clear (maybe necessary design choices to make the computer cheaper, or an attempt to break with former design choices, or a marketing issue). As a consequence, you cannot run TO7/70 programs on a MO5 (except pure BASIC programs, supposing that you do not load them from a cassette but, e.g., from a floppy). Interestingly enough the floppy controller is the same as the TO7 one (its ROM has been designed to work for both families).

It was a main component of the government plan "Informatique pour tous" (i.e., "Computer Science for Everyone"). Many MO5 (and a few TO7/70) were bought by the government and put in schools to teach computer science to children. Such computers were connected into networks (unfortunately, network is currently not emulated in MESS, but I hope to get it working at some point.) Thus, it featured a lot of educational software. It was also a great game computer until the TO8 was built.

Unlike the TO7 cassette format, the MO5 cassette format is a quite simple MFM encoding (Modified Frequency Modulation) and is decoded fully in software. This gave rise to variants: many games were encoded specially and used a special loader in order to prevent people from disassembling the raw files. Some emulators use a byte-based format that cannot represent these protections, and so, rely on emulator-specific hooks. These hooks are not emulated in MESS. Thus, you should prefer raw .wav files that faithfully emulate protection schemes in MESS. Note that byte-based images often use the suffix .k5 to differentiate them from TO7 files, but many also have a .k7 suffix which is confusing because they cannot be run on a TO7.


This MESS driver was written by Antoine Miné.

Return to the 8-bit Thomson MESS driver page.