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Z80 - mc-2g-1024

The specifications are:

  • New ROM monitor with multi-boot capability, Format, Getsys and Putsys tools and debug capabilities. No BASIC in ROM.
  • SD-HC capable card controller running at 25 MHz.
  • CPU clock running at 25 MHz
  • Multi volume disk system, which currently supports upto 254 8MB disk volumes (which uses 2GB+ on the SD-card). All these volumes can be loaded with a separate OS bootimage.
  • OSes configured with 3 drives: A:, B: and C:. A: is the system drive (holding the volume booted from) while B: and C: can be assigned and re-assigned one of the remaining volumes. Also a RAM disk for CP/M 2 and CP/M 3
  • Y2k compatible system clock (date and time) for all OSes.
  • mc-2g-1024 on retrobrew site
  • Supports:
    • Dos+ 2.5
    • CP/M 2.2
    • CP/M 3.1
    • ZSDOS 1.1 / ZCPR2
    • ZPM3 /ZCCP
    • NASCOM “ROM” BASIC 4.7

Banked Memory

  • The system supports upto 1024 KByte of SRAM in 512 KByte increments
    • This SRAM is divided in 16 kByte frames.
    • The system memory uses segments 0-3, in which frames 0-31 (or 0-63 for 1024 kByte systems) can be mapped.
  • CP/M 3 uses 2 segments per bank (32 kBytes) and requires only 128 kBytes to run
  • This OS will not natively use the extra memory for anything else but bufferspace.
  • MP/M 2 uses 3 segments per bank (48 kBytes).
    • It will run in 128 kBytes, but only 1 full 'extra' bank will be available.
  • MP/M uses the extra memory as user TPA.
    • Using more than 512 kByte is pointless, MP/M is limited to 7 extra banks.
  • In CP/M 2 and CP/M 3 variants the extra SRAM (frame 9-31 or 9-63) is used as a ramdrive (M:)


  • The CP/M2 and CP/M3 variants support a ramdisk, either 384kB (in s 512k system) or 896 kB (using 1024 kB SRAM).
    • This size is adjusted by the BIOS.
    • The contents, once initialized with RDINIT.COM, persists as long as the board remains powered, with one caviat: MP/M uses this memory too, so booting MP/M overwrites part of the memory used for the ramdisk.
  • MP/M does not (yet) support a ramdisk.

S1 - CP/M 2.2 - Dos+ 2.5 - CCP+ Ver 2.2

  • This is an unpatched implementation by C.B. Falconer's Dos+ version 2.5.
    • Please read the documentation to switch on the optional features.
  • Because this OS treats console input differently (it checks for user breaks after each character it outputs) the original DOWNLOAD.COM no longer works.
    • It was modified to use direct BIOS I/O to circumvent the above behaviour, but because after every file the command prompt is displayed some characters are still lost.
    • This is circumvented by padding the input file with enough spaces to make up for the lost characters.
    • This version of DOWNLOAD.COM also works under CP/M 2.2 and CP/M 3.
      • A way to work around this is to just download all the files you want under CP/M 2.2 to the target disk mounted as B: or C:
  • Dos+ implements a search path which is initialized by the command STARTUP.COM.
    • STARTUP.COM is automatically run when the system is first booted.
    • STARTUP.COM can be any .COM command you like, as long as the name does not change.
  • Mounting drives is done with the MOUNT.COM tool.


SD Vol 001.png

S2 - CP/M 2.2

  • This OS is as was provided by Grant Searle.
    • It uses a new BIOS, providing mountable volumes, a Ramdisk and a clock.
    • All Grant's tools work as intended, in particular the original DOWNLOAD.COM.
  • The start address for the initial download of "DOWNLOAD.COM" (backdoor startup) from the provided .HEX file has changed to FFFB.


SD Vol 002.png

S3 - CP/M V3.0


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S4 - MP/M II V2.1

  • MP/M also boots a loader, which in turn loads MPM.sys from the chosen volume.
  • The XIOS also supports mountable diskvolumes, however these can be asigned only during a cold boot.
    • The mounting mechanism is similar to the CPM-2 version, but an easy vector to the mount table is not implemented.
    • Although this is doable, changing volumes in a multi-user environment should be avoided.
  • The BIOS supports 4 consoles.
    • Using the GENSYS.COM tool this number can be changed.
    • It is OK to connect less consoles than configured, but this will use system resources (memory and processor time).
  • MP/M XIOS is currently a vanilla implementation straight from Digital's documentation.


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S5 - Z80 BASIC


S6 - CP/M 2.20 - ZSDOS v1.1

  • ZSDOS is a CP/M 2.2 variant, but it requires a modified BIOS.
    • The changes include a modified time and date routine as well as increased bufferspace for the various ZCPR features.** Also a "HighMemory" buffer for the time/date driver and timestamper routine is provided. (see sourcecode for details).
    • The included LDTIM.COM routine loads the driver to the correct location.


SD Vol 006.png

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S7 - CP/M V3.0 - ZPM3 / ZCCP

  • ZPM3 is CP/M-3 variant, which uses the same BIOS code as CP/M-3.
    • A rudimentary NAMES.NDR file was included to jump-start the "named directory" feature.
    • A TCAP.Z3T for use with a DEC VT-100 terminal is also present.
      • A working TCAP is needed for many of the ZPM3/ZCCP user programs.



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S9 -






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S10 -






S11 -