Instruction manual

CMMND1: LD SP,CCPSTACK ;set stack straight.

CALL CRLF ;start a new line on the screen.

CALL GETDSK ;get current drive.

ADD A,'a'

CALL PRINT ;print current drive.

LD A,'>'

CALL PRINT ;and add prompt.

CALL GETINP ;get line from user.

;

Change the character in the ADD A,'a' instruction to an upper case A:

;

CMMND1: LD SP,CCPSTACK ;set stack straight.

CALL CRLF ;start a new line on the screen.

CALL GETDSK ;get current drive.

ADD A,'A'

CALL PRINT ;print current drive.

LD A,'>'

CALL PRINT ;and add prompt.

CALL GETINP ;get line from user.

;

Assemble to a binary output file cpm22.sys. This file contains the machine code for the CP/M Console

Command Processor (CCP) and Basic Disk Operating System (BDOS).

The third part of CP/M, the customized Basic Input Output System (CBIOS) for the CPUville system

with the Disk and Memory Expansion, I have written and assembled for you. You can download the

CBIOS source and binary files, and other binary helper files mentioned below, from the CPUville web

site. The binary file for the CBIOS is z80_cbios.bin. The other files you will need are format.bin,

putsys.bin, cpm_loader.bin, and monitor.bin.

Preparing the disk for CP/M

The CP/M file system directory entries are very simple. The first byte of a directory entry gives the

status of the entry. If the entry is inactive (the file has been deleted or not yet created), the status byte

has a value of 0xE5. To prepare a disk for the CP/M system, one needs only create a number of

directory entries that start with this value.

But it is easier than that, because if a directory entry is inactive, CP/M does not care what else is in the

directory. It will create a completely new entry when it needs to. So, all we need to do is write the value

0xE5 to all the sectors of the CP/M disk in order to prepare it.

Note that I refer to the “CP/M disk”. This is a logical construct, created by the disk parameter tables in

the CBIOS. These tables may or may not accurately represent the physical disk system. In the CBIOS I

created, I left the CP/M disk system as it originally was, with four disks, each with 77 tracks, 26 sectors

per track. A CP/M call to read or write a particular disk, track, and sector is translated into a unique

LBA address for the hard disk by the disk read and write subroutines in the CP/M CBIOS.