Using TR-DOS Disks on the Pentagon 128

The Pentagon 128 model (Machine ID sp128, model pentagon) has the Beta 128 disk interface, the Pentagon’s own disk system: a floppy disk controller, two drives (A and B) and the TR-DOS disk operating system. Much Pentagon software, from demos to games and disk magazines, comes on TR-DOS disks.

Naming your TR-DOS ROM

With the Pentagon selected, open Machine > TR-DOS ROM in the Emulator window:

• Select TR-DOS ROM File… picks the image. It must be exactly 16,384 bytes. The machine restarts with it.
• Forget the TR-DOS ROM clears it.

The first item of the submenu says which ROM is in use, or that none is set. Without a ROM the Pentagon still runs, but its drives are off. The ROM is a Klive setting, not a project setting, so you name it once.

Inserting disks

Machine > Floppy Disks works as it does on the ZX Spectrum +3: Insert Disk into Drive A… (or B), Eject, and Write Protect. The emulator’s media strip shows both drives. The Pentagon takes:

• .trd files: raw TR-DOS disk images. When TR-DOS writes to the disk (SAVE, FORMAT, ERASE…), Klive writes the changed sectors back into the .trd file.
• .scl files: compact archives of TR-DOS files. Klive builds a disk from them when you insert one. TR-DOS can write to that disk, but the .scl file is never changed. To keep the changes, use Save Disk in Drive A as .trd…, which writes a new .trd and puts it in the drive.

Create Disk File… makes a blank, formatted TR-DOS disk (80 or 40 tracks, one or two sides), as does the IDE command crd, for example crd trd80ds games.

Booting a disk

Machine > Floppy Disks > Boot Disk in Drive A resets the machine and does what you would type: it selects 48 BASIC from the 128K menu, enters TR-DOS with RANDOMIZE USR 15616, and types RUN, which loads and runs the disk’s BASIC program boot.

You can also do it by hand. At the TR-DOS A> prompt, the usual commands work: LIST shows the catalogue, RUN "name" and LOAD "name" load files, SAVE "name" CODE 32768,100 saves one, and RETURN goes back to BASIC. From a BASIC program, RANDOMIZE USR 15619: REM : LOAD "data" CODE runs a TR-DOS command.

Debugging with TR-DOS

While TR-DOS runs, its ROM replaces the 48K BASIC ROM at $0000. The debugger shows it as the memory partition R2 (“TR-DOS ROM”), so a breakpoint like R2:$3D2F stops only in TR-DOS.

Snapshots and machine states

• A .szx snapshot of the Pentagon keeps the disk interface’s state and links the disks to their files. A .sna keeps only whether TR-DOS was paged in; a .z80 keeps neither.
• A snapshot taken with TR-DOS paged in opens on the Pentagon.
• A machine state keeps the disks with everything written to them. After you load one, the disks are not written back to their files until you insert a disk again.