Dobbertin CPM+

Dobbertin implemented their own CPM+. The sign on message displays "CP/M Plus Amstrad Consumer Electronics plc".

Their CPM+ has:

• detects on boot if there is at least 128KB memory and error if there isn't.

• a RAM-Disk

This uses a Dk'tronics/Dobbertin RAM expansion. It doesn't support Vortex RAM expansion. The size of the RAM expansion is auto-detected allowing ram disk sizes of 62KB, 190KB, 254KB, or 444KB. These correspond to 256KB RAM, 256KB Silicon Disk and combined RAM and Silicon Disk (512KB RAM) expansions. The Ramdisk is accessible in CPM+ with drive C.

• support for their HD20 Hard disk

This requires a HD20 capable X-DDOS because it checks for a specific variable set by X-DDOS if it detects the hard-disk. The main hard disc functions are in bank 0, with common hard disk buffer read/write in the common C7 bank at &FE00. The hard disc is accessible in CPM+ with drive D,E,F and G.

• supports both 50hz and 60hz displays.

If 60hz is detected the Vertical Sync is set to 16 lines and the hsync is set to 4. Otherwise it remains unchanged.