Background

Like the majority of home computers of its day, the original MTX used compact cassette tape for offline storage, however, it was not a viable, nor indeed desirable, option for MTXPlus⁺.

There are a number of formats that could have been considered for use as the removable media system, including SD card like Andy's REMEMORizer, but, given that Lez had included Compact Flash readers in the parts kits that he donated, this was the logical choice. In addition, Lez had also included a number of 8255 PPI (Programmable Peripheral Interface) chips in the kit and there were proven instances of using the PPI with CF available on the internet.

 

Media Format

Open a windows command prompt with Administrator privileges, and at the command prompt, enter :

format <drive letter>:  /FS:FAT32

For a full list of format options, enter :

help format, or, format /?

File Formats

The majority of Memotech MTX software is already available in a number of different formats, including tape files (".mtx"), sound files (".wav", ".mp3) etc. Andy has a good explanation of the various file formats on his site, but in brief, the files are predominantly available in the following types :-

The most convenient way to have MTX BASIC use the CF interface for file loading and saving was to modify the existing BASIC tape commands, "LOAD", "SAVE" and "VERIFY". Martin patched the existing ROM and added new code in the MTXPlus⁺ support ROM to control the CF interface from MTX BASIC.

Some compromises had to be made to enable the CF media to be used from both MTXPlus+ and other CF hosts such as PCs running Windows.

File Naming Convention

The default filename format under FAT32 is the same as the original FAT format, i.e., 8.3. FAT32 volumes can also use long filenames that can be fully utilised under, for example, Windows 7. MTX BASIC allocated up to 16 characters for tape filenames, we decided that MTXPlus⁺ would use the 8.3 naming convention and throw away the additional 4 characters available to MTX BASIC.

Subdirectories

MTXPlus+ supports directories on the CF card, there isn't a hard limit on the number of files that can be read or written to the root or other directories on the card from MTXPlus+, but I can't see the value in having lots of files in a single directory. To make directory listings easier to read, when the user lists the files in a directory, they are sorted alphabetically before being displayed.

The directory sorting code uses a fixed size (32k) RAM buffer that has been allocated for the CF card, the size of the buffer allows ~1000 files in a single directory to be sorted - this should be more than adequate. However, if the number of files is greater than this, only the first 1000 or so will be sorted.

To simplify the ROM changes required to support subdirectories, FAT entries containing only a filename with no suffix, e.g., "RUN", are deemed to be subdirectories.

MTX BASIC CF Commands

The MTX ROM has been patched such that the MTX BASIC LOAD "<filename.ext>" command loads a file from the CF card. Currently supported file types are  .run and .mtx, the file extension must be specified so that the ROM knows how to handle the loaded data.

To provide the ability to list the contents of the CF card, the LOAD "" command has been modified such that it lists the contents of the CF card, rather than loading the first file found on the media as the standard MTX would. The default directory listing is a sorted list of the files & directory names in 8.3 format.

An extended directory listing, showing, filename, modification date & time and size is available by using the SAVE "" command.

 

MTXPlus⁺ BASIC Compact Flash Commands

Status Update

The FAT32 filing stucture was eventually dropped and MTXPlus+ now uses the CP/M file structure used in the original Memotech disk drives and in Andy Key's REMEMOTECH and REMEMOrizer systems.