HOW TO BUILD A NEW CP/M

Note: with 64K of RAM, the largest CP/M may be less than 64K, depending on the size of your BIOS. My own MBIOS requires different amounts of RAM depending in version:

 * Version 3.xx:  62K CP/M
 * Version 4.xx:  55K CP/M (because of the track buffer)
 * Version 5.xx:  63K CP/M (The track buffer is in its on RAM bank)

1) Assemble your BIOS with the desired CP/M-standardized memory size

a) in MBIOS.ASM, set the MSIZE variable to position CP/M where you want it. Rename this file MBIOS63.ASM.

  MSIZE	equ	63	;CP/M standard memory size in Kbytes

b) ASM MBIOS63

(This creates MBIOS63.HEX.)


2) Use MOVCPM.COM to create a bare CP/M image of the matching size.

How to use MOVCPM, avoiding their copy protection

  >DDT MOVCPM.COM
  -S234
  0234 C2 0
  0235 5A 0
  0236 02 0
  0237 02 .

  -S2CB
  02cB C2 0
  02CC 5A 0
  02CD 02 0
  02CE .

  I63 *   <----{This example tells MOVCPM.COM to build a 63K CP/M image}
  -G

  CONSTRUCTING 55k CP/M vers 2.2
  READY FOR "SYSGEN" OR
  "SAVE 34 CPM63.COM"

>SAVE CPMDR63.COM

(This creates CPMDR63.COM.)


3) Assemble the boot loader for the correct memory size

a) In MEBOOT.ASM, set the MSIZE variable to match the value given to MOVCPM.COM. Rename this file MEBOOT63.ASM

  MSIZE	EQU	63		;MEMORY SIZE IN KILOBYTES

b) ASM MEBOOT63

(This creates MEBOOT63.HEX)

4) Calculate/look up the address offset for the BIOS

  CP/M Size  Offset   CP/M Size  Offset   CP/M Size  Offset
     20K      D580       52K      5580       59K      3980
     24K      C580       53K      5180       60K      3580
     32K      A580       54K      4D80       61K      3180
     40K      8580       55K      4980       62K      2D80
     48k      6580       56K      4580     >>63K      2980<<
     50K      5D80       57K      4180       64K      2580
     51K      5980       58K      3D80


5) Combine the relocated CP/M with the New BIOS and boot loader

  >DDT CPMDR63.COM

  -IMEBOOT63.HEX

  -R880

  -IMBIOS63.HEX

  -R2980      <----This is the BIOS address offset from step 4

  -G0

6). Use MSYSGEN.COM to write the version of CP/M that's in the RAM buffer to the disk's system area. (skip loading the CP/M image bewcause your new CP/M image is already in RAM.)