CP/M 3.0

CP/M 3.0 after boot

CPM 3.0 (also known as CPM+) was available on the 2nd System Disc for CPC6128 but there were other implementations available.

Graduate Software's implementation of CP/M+ on ROM

• Graduate Software

Amstrad's implementation of CP/M+

Amstrad distributed CP/M+ on the side 4 of the system discs that came with the CPC6128. It requires a Dk'Tronics compatible ram expansion. It provided 61K TPA. To get 61K TPA, CPM+ uses 'C1' and 'C2' RAM configuration with TPA in the 2nd bank and the CCP, BDOS, BIOS, screen and firmware in the 1st 64KB of RAM. This arrangement allows 61KB useable for programs.

On side 1 of the system discs was CP/M 2.2.

• Amstrad CP/M+ uses Amstrad's "System" format. This is 40 tracks, 1 side, 9 sectors per track numbered &41-&49. Each sector is 512bytes. There are two reserved tracks, then the directory which has 64 entries (which occupies 4 sectors) and then the data area.
• CP/M is booted using an RSX command "|CPM" which is implemented in the Amstrad disc rom (AMSDOS).
• |CPM loads track 0, side 0, sector &41 into RAM at &100-&2ff. This is the boot sector and contains the boot program.
• The boot program then loads the directory from track 2, sector &41.
• The boot program locates a program with extension "EMS".
• This program is loaded into RAM at &c00.
• This is then executed. (EMS contains the BIOS, BDOS and relocates and re-configures the memory. CP/M doesn't use the CP/M 2.2 BIOS from the Amstrad disc ROM.)

Memory layout

• 1st 64KB has the CCP, BDOS, BIOS, screen and firmware. Screen is at &4000-&7fff. Firmware is used. AMSDOS is not used.
• There is some trampoline code at &c000-&ffff. C1 configuration is used. (this has C7 at &c000-&ffff)
• 2nd 64KB has the TPA and complementary trampoline code. c2 configuration is used.

a) Page C4 has WBOOT and BDOS jump + &100-&3f00 of the TPA. This calls to functions in Page c7. b) Page C5 has &4000-&7fff of the TPA. c) Page C6 has &8000-&bfff of the TPA. d) Page C7 has &c000-&f2fb of the TPA. From &f2fc to &ffff is the trampoline code which transitions * to 1st bank of 64KB.