Introduction to CP/M on the 128

[Blacklord]

What is CP/M?

CP/M stands for 'Control Program/Monitor'.  It is not a
programming language, the way BASIC or Fortran is, but a micro
computer operating system, much like the KERNAL used in C-128
native mode and other 6502 based Commodore computers.  CP/M was
developed in the 1970's by Digital Research Inc.  (DRI) for Intel
8080 micro processor based computers that allows a given program
to run on a wide variety hardware configurations with little or
no changes.  It was later extended to run on Zilog Z80 based
computers as well as others.  (The Z80 used in the C-128 is
'upwardly compatible' with the 8080.  That is, its machine
language instruction set includes everything that the 8080 has
and more.)  With CP/M, a software developer has a uniform set of
basic operating system functions to work with (such as screen
output, keyboard input and disk access routines).  To the end
user, these system functions remained fixed, no matter what
computer the program is actually running on, thus providing a
very high degree of portability.  (You need only develop one
version of a program which operates under the CP/M system instead
of having a different version for brand x, y, and z computers.)
For those who may be interested, there is also a 16-bit version
of CP/M designed to run on 8086/88 type computers called CP/M-86,
a multi user version called MP/M and a 16/32 bit version for the
MC68000 chip series called CP/M-68k.

CP/M is divided up into four main components:  the BIOS (Basic
Input Output System); the BDOS (Basic Disk Operating System), the
CCP (Console Command Processor) and the TPA (Transient Program
Area).  Each of these parts will be discussed in later chapters.
Of the four parts, only the BIOS is hardware dependent.  It acts
as the messenger between the other parts of the system and the
actual hardware.  That is, a separate custom BIOS must be created
for each system that runs CP/M.


CP/M on the C-128

The version of CP/M used on the C-128 is termed 'CP/M Plus' or
'CP/M version 3'.  This is the latest 8-bit CP/M version, and is
also used on other recent CP/M based computers such as the Epson
QX-10, and TRS-80 Model 4.

The minimum configuration for running CP/M on the C-128 is the C-
128, one disk drive, and a 40 or 80 column monitor.  For speed
and ease of use, a fast disk drive (i.e. the 1571 or 1581) is
recommended along with the 80 column monitor.  For disk intensive
programs (many CP/M programs are), a 1700 or 1750 RAM expansion
unit is highly recommended as it can be used as a super fast RAM
disk.  A printer (device 4 or 5) along with a modem will round
out your system.  (Use of the modem requires CP/M release dated
DEC 85 or later.)

To start up CP/M on the C-128 or 128 D, put the CP/M BOOT disk in
disk drive device 8 and turn on the drive and then the computer
(in that order).  If the computer and drive are already on,
insert the boot disk, then press the reset button on the C-128 or
type in BOOT followed by pressing the <return> key.  After a few
moments and some sign-on status message screens, you will see a
prompt on the screen in the form of the letter A followed by a
'greater than' sign and a flashing cursor.  (A>_)

Congratulations!  You have just started up CP/M successfully and
are ready to enter your first CP/M command.  Just for fun, type
in the letters D I R then press the key marked <return> at the
right side of the main keyboard.  A 'directory' or 'catalog' of
the contents of the boot disk should be displayed on the screen.

The Status Line

The bottom line of the screen display (i.e. the 25th line) on
either the 40 column or 80 column screen is used by CP/M as a
status line to display various system messages.  These are outlined
below.


Disk Status

C-128 CP/M has an optional disk status window displayed at the
bottom right corner of the screen.  The format of the status window
is as follows:

                                   O Dtt ss

where:      O     =Operation, either R or W indicating a Read or Write

            D     =the logical drive (A,B,C,D, etc)
            tt    =the track number currently being read or written
            ss    =the sector number currently being read or written

Normally,  the track and sector numbers are separated by a space.
If the disk is formatted in MFM,  and the track and sector are
separated by a '-', then the second side of the disk is currently
being accessed.

You  can toggle this status window on or off by typing  the
<CONTOL>-<RUN/STOP>  key key combination.  Note that window is also
erased temporarily, i.e. until the next disk access, when you (or
your application program) perform a screen clear.

The disk status window is not used for RAM disk operations (i.e.
1700/1750 RAM expansion unit).  You may also note that, due to a
bug in the fast bus GCR sector translation routine, the sector
numbers displayed during reading and writing of both single and
double sided C-128 native GCR type CP/M disks are incorrect when
using a 1571 drive.  Correct numbers are, however, displayed when
using a 1541 drive to access these disks.


MFM Disk Type Selection

C-128 CP/M supports a number of industry standard MFM disk types
(such as KayPro, Osborne, IBM, Epson, etc.) when used with a 1571
disk drive.  However, CP/M sometimes cannot automatically
distinguish between two very similar disk types such as KayPro II
and KayPro IV.  For example, although the KayPro II is a single
sided disk and the KayPro IV is a double sided one, CP/M can
confuse the two because both have ten sectors of 512 bytes per
track, numbered 0 to 9 on side 0.  CP/M looks at the physical
format of side 0 to determine the foreign disk type.  When two or
more matches are found in its internal parameter table, you are
asked to manually chose which one you want.

When CP/M cannot uniquely identify the foreign disk format being
accessed, the program will pause momentarily and the disk type
window will open up at the center of the bottom line of the screen
to display the name of the first match, such as KayPro II, in
reverse video.  At this point there are several things that you can
do.

First, if you are sure that the disk is of the type displayed,
simply press <return> or <enter>.  This will select the currently
displayed entry.  If you change disks, you will have to go through
the selection process over again.

Second, if you are going to be using this disk format repeatedly
and do not wish to re-select each time you change disks, you can
'lock in' the selected type by pressing <control>-<return>.  This
action has the effect of performing a burst mode 'forced login' on
the drive each time you change disks.  If you insert a new type of
disk while locked in, you will go back to the selection window.

Note:       The forced login commands are different for the 1571 and
            1581 drives and therefore, <control>-<return> should not
            be used with a 1581 drive.  If you do use it on a 1581
            and change disks, the results may be unpredicatble, even
            resulting in system crash.

The third option is used to display and select the alternate disk
choices.  Use the cursor left and cursor right keys in the cursor
control keypad (above the main keyboard) to scroll through the list
of choices.  In the example used above, the display should change
between KayPro II and KayPro IV.  When the correct entry is
highlighted, you can use either of the two methods outlined above
for making the selection.  Note that because you are in a suspended
program loop, nothing else can be done until you make a selection.


PAUSE

The  key  labelled NO SCROLL executes a PAUSE function.  Although
this key appears to have the same effect as typing <control>-s
(stop) and <control>-q (start) for pausing to read screen dumps, it
is not actually related in terms of the internal workings of the
operating system.  Using NO SCROLL sends the program into an
endless loop while displaying the message 'PAUSE' on the status
line.   Because of this, NO SCROLL cannot be used to pause a
display before pressing <control>-p to toggle the printer, or
<control>-c to abort execution of a program.

To resume execution after a PAUSE function, press NO SCROLL again
(for AUG or DEC release only) or RETURN (for MAY release only).  


Disk Drives

C-128 CP/M supports a variety of different disk drives (virtually
any serial bus drive is either supported directly or can be easily
adapted).  However, since CP/M tends to be a disk intensive
operating system (i.e. it makes heavy use of temporary disk files,
overlay files, working files, etc.), a fast bus drive (i.e. a 1571
or 1581) is highly recommended for maximum disk access speed.

CP/M in general can support up to 16 disk drives, usually labelled
A: to P:.  On the C-128 implementation, normally only a maximum of
6 drives are actually supported.  In the default system
configuration, these are:

DRIVE             DEVICE

A:          serial port device 8, drive 0
B:          serial port device 9, drive 0
C:          serial port device 10, drive 0
D:          serial port device 11, drive 0
E:          serial port device 8, drive 0  (see 'Virtual Disk Drive'
            below)
M:          17xx RAM expansion unit  (see 'RAM Disk' below)



Virtual Disk Drive

The  physical disk drive A can be used as logical drive A or as the
'virtual' or 'phantom' logical  disk drive E.  Whenever  you
access drive E (for example by doing DIR E:, or PIP E:=A:FILE1),
the system will display a prompt on the status line asking you to
insert the diskette for drive E (respond by putting whatever
diskette you want into physical drive A,  then type <return>).
The next time you access logical drive A,  the  system will prompt
you to insert the A diskette in drive A.  Again, insert the desired
diskette and type <return>.  Note that CP/M does not actually check
to see if you in fact changed the disk.  It will accept whatever is
in the drive when you press <return> as being the correct disk.


RAM Disk

When the 1700 (128k byte) or 1750 (512k byte) RAM expansion unit
(REU) is connected to the C-128 in CP/M mode, it becomes an ultra
fast RAM disk, normally assigned to CP/M drive M:.  That is, any
CP/M command or transient utility can access the REU as drive M:,
just like it can any other 'disk drive' connected to the system.
Note that this is totally separate from the virtual disk drive
discussed above.

Unlike a physical disk drive, the contents of the RAM disk are not
preserved when the C-128 is turned off.  However, the contents are
preserved when the reset button is pressed momentarily to re-boot
the system, even if you enter C-128 native mode or C-64 mode before
returning to CP/M mode (providing, of course, you do not alter the
contents either accidentally or intentionally by running some other
program while in one of these other operating modes).

Note that in order to use the RAM disk, you must have the C-128
CP/M release dated 6 DEC 85 or later.


The Screen

C-128 CP/M supports both the 40 column and 80 column display
screens.  The screen which is initially active is determined by the
position of the 40/80 switch on boot up.  After booting, the screen
can be selected using the DEVICE utility (see Chapter 3) or
equivalent.  The screen can be changed during the execution of a
user program by setting the CONOUT redirection flag in the system
control block (see Chapter 9).

The 40 column screen is configured as a window on a larger 80
column 'virtual' screen.  This allows commands and programs to
think that they are dealing with an 80 column wide screen (the
default width for most CP/M programs). Use <control>-<left arrow>
and <control>-<right arrow> to scroll the window across the virtual
screen (see Arrow Keys, below).


Printer Support
     
C-128 CP/M can support two printers, serial port devices 4 and 5.
In its default configuration, device 4 (CP/M physical device
PRT1) is assigned to the logical LIST device with a secondary
address of 7 and ASCII to PET-ASCII translation enabled.  To
change to a device 5 printer, use the DEVICE utility (see Chapter
3).  To disable ASCII to PET-ASCII translation, use the CONF
utility.


The Keyboard

The operation of the C-128 keyboard is slightly different in CP/M
mode than it is in native mode.  For one thing, it uses the
standard 7 bit ASCII character set rather than the PET-ASCII set
used in native mode.  In addition, each key is completely
programmable as to its character codes or other special
functions.   Other differences in keyboard operation are outlined
below.


Alpha Keys

The alpha keys on the main keyboard (e.g. A, B, C, D, etc.)
generate the standard lower case,  upper case, CAPS LOCK and
control values.  The CAPS LOCK value defaults to the upper case
value and is used as a software shift lock.  It is not related to
either the SHIFT LOCK key or the CAPS LOCK key.  To turn the CAPS
LOCK mode on, press the Commodore logo C= key at the lower left
of the main keyboard.  Pressing the same key again, will turn off
CAPS LOCK mode.


Numeric Keys

The numeric keys (the row of keys above the alpha keys) produce
the appropriate number as the unshifted value and the CAPS LOCK
value,  the symbol above the number on the key as the shifted
value and the color on the side of the key (the top one of the
two colors shown) as the control value.   These colors are
defined as 80 column foreground colors.   The control value
produced by the numbers on  the numeric keypad are defined the
same as those on the numeric keys,  except that they generate 80
column background colors.

 
Arrow Keys

The arrow keys are located in the cursor keypad above the top
right portion of the main keyboard.  The functions and character
codes assigned to these keys in CP/M mode are different to those
assigned to the cursor control keys at the lower right of the
main keyboard.  The default values for the arrow  keys are those
use used by most application programs which feature full screen
cursor movement, such as text editors, etc.

The up arrow key generates the value 05 (<control>-e) as the
unshifted, shifted and  CAPS LOCK  values;   it generates the
hexadecimal  12  (<control>-r) as the control value.

The down arrow key generates the hexadecimal value 18 (<control>-
x) as the unshifted,  shifted and CAPS LOCK values; it generates
the value 03 (<control>-c) as the control value.

The left arrow key generates the hexadecimal value 14 (<control>-
s) as the unshifted,  shifted and CAPS LOCK values;  it executes
the 40 column screen left function as the control value.

The right arrow  key generates the value 04 (<control>-d) as the
unshifted,  shifted and CAPS LOCK values;  it executes the 40
column screen right functions as the control value.


Additional ASCII Characters

The  key labelled as a British pound sign generates the character
'#' as  the unshifted, shifted and CAPS LOCK values.   The
reverse apostrophe character ` is generated as the control value.
 
The  up arrow key next to the <RESTORE> key generates the caret
character '^' as the shifted and control values.   The pipe
character '|' is generated as the  unshifted and CAPS LOCK
values.

The  '='  key  generates  the character '='  as  the  unshifted,
shifted and CAPS LOCK values.  The tilde character '~' is
generated as the control value.

The  '/'  key  generates  the character '/'  as  the  unshifted,
shifted and CAPS LOCK values.  The back slash character '\' is
generated as the control value.

The  key labelled 'INST DEL' generates the hexadecimal value 7f
(ASCII rubout) as the unshifted, shifted and CAPS LOCK values;
the hexadecimal value 16 (<control>-v) is generated as the
control value.


Special Key Functions

The  key  labelled NO SCROLL executes a PAUSE function.  To
resume execution, press NO SCROLL again (for AUG or DEC version
only) or RETURN (for MAY version only).   The control value of
the  NO  SCROLL key toggles between two modes (on/off) of
automatically tracking the CP/M screen on a 40 column monitor.

The  right and left arrows at the top of the keyboard initiate
the special functions screen right  and  screen  left
respectively  (40  column  screen tracking) as their control
values.

The key labelled <ENTER> generates a Carriage Return as the
unshifted, shifted and CAPS LOCK values.   The control value
initiates the special function boot, which reboots the system as
if the reset button has been pressed.  If a CP/M boot disk is in
drive A:, the CP/M system will be re-started, otherwise normal C-
128 native mode will be started.

The key labelled <RUN/STOP> is undefined as its unshifted,
shifted and CAPS LOCK values,  and  toggles the
display/nondisplay of the disk status window as its control
value.

The  key  labelled  CRSR with up and down arrows (bottom right on
main keyboard) generates  the hex value 17 (<control>-w) which
causes the latest CP/M command line to be re-typed on the screen.
The key next to this (CRSR with right and left arrows) allows you
to move right (<control>-f) and left (<control>-a) (unshifted and
shifted, respectively) through a command line to edit it.

The key labelled F1/F2 generates the two character string 'F1' in
the unshifted and CAPS LOCK modes and the string 'F2' in the
shifted and control modes.

The key labelled F3/F4 generates the four character string 'dir
<return>' in the unshifted and CAPS LOCK modes and the string
'dir' in the shifted and control modes.

The key labelled F5/F6 generates the two character string 'F5' in
the unshifted and CAPS LOCK modes and the string 'F6' in the
shifted and control modes.

The key labelled F7/F8 generates the two character string 'F7' in
the unshifted and CAPS LOCK modes and a string representing the
date that the system files were assembled in the shifted and
control modes (i.e. the date which is displayed in the sing-on
message).

The key labelled HELP generates the string 'Help' in all modes.


     



The Command Line
 
CP/M commands and transient programs are accessed from the system
prompt by typing in a sequence of characters called a command
line.   A CP/M command line is composed of a command,  an
optional command tail, and a carriage return.  The command is the
name or filename of a program to be executed.  The optional
command tail can consist of a drive specification, one or more
file specifications, and some options or parameters.


        A>COMMAND {command tail} <cr>


               
Command Conventions

The following special symbols define the syntax of a normal
command line.

      {}          surrounds an optional item.
      |           separates alternative items in a command line.
      <cr>        indicates a carriage return.
      ^           indicates the Control Key.
      n           substitute a number for n.
      s           substitute a string (group) of characters for s.
      o           substitute an option or option list for o.
      []          type square brackets to enclose an option list.
      ()          type parentheses to enclose a range of options
                  within an option list.
      RW          Read-Write attribute - opposite of RO
      RO          Read-Only attribute - opposite of RW
      SYS         System attribute - opposite of DIR
      DIR         Directory attribute - opposite of SYS
       ...        preceding element can be repeated as many times as
                  desired.
      *           wildcard: replaces all or part of a filename
                  and/or filetype.
      ?           wildcard: replaces any single character in the
                  same position of a filename and/or filetype.


Command Line Editing

The resident CP/M command interpretter (CCP) allows a certain
degree of editing of the CP/M command line before pressing the
<return> key.  The editing keys are outlined below along with
their usage.  It should be noted that these editing keys are
totally independent from the control codes used by the terminal
emulation for the video display.


  Control Character           Function

  CTRL-A                moves cursor one character to the left.

  CTRL-B                moves cursor from beginning to end of command
                        line and back without affecting command.
 
  CTRL-C                stops executing program  when  entered  at
                        the system prompt or after CTRL-S.

  CTRL-E                forces a physical carriage return without
                        sending command.

  CTRL-F                moves cursor one character to the right.

  CTRL-G                deletes character at current cursor position
                        if in  the middle of a line.

  CTRL-H                delete character to the left of cursor.

  CTRL-I                same as the TAB key.

  CTRL-J                moves cursor to the left of the command line
                        and sends command to  CP/M.  Line  feed,  has
                        same effect as carriage return.

  CTRL-K                deletes character at cursor and all
                        characters to the right.

  CTRL-M                same as carriage return.

  CTRL-P                echoes console output to the list device.

  CTRL-Q                restarts screen scrolling after a CTRL-S.

  CTRL-R                retypes the characters to the left of the
                        cursor on a new line; updates the command
                        line buffer.

  CTRL-S                stops screen scrolling.

  CTRL-U                updates the command line buffer to contain
                        the characters to the left of the cursor;
                        deletes current line.

  CTRL-W                recalls previous command line if current line
                        is empty; otherwise moves cursor to end of
                        line.  CTRL-J,-M,-R,-U and RETURN update the
                        command line  buffer  for  recall  with CTRL-
                        W.

  CTRL-X                deletes all characters to the left of the
                        cursor.


Filespec

CP/M identifies every file by its unique file specification,
which can consist of four parts:

            the drive specification,
            the filename,
            the filetype and
            the password.  

The term "filespec" indicates any valid combination of the four
parts of a file specification, all separated by their appropriate
delimiters.  A colon must follow a drive letter.  A period must
precede a filetype.  A semicolon must precede a password.

The general symbols and rules for the parts of a file
specification follow:

  d:              drivespec   optional    single alpha character (A-P)
  filename        filename                1-8 letters and/or numbers
  typ             filetype    optional    0-3 letters and/or numbers
  password        password    optional    0-8 letters and/or numbers

If you do not include a drive specifier, CP/M automatically uses
the default drive. Valid combinations of the elements of a CP/M
file specification are:

                filename
                d:filename
                filename.typ
                d:filename.typ
                filename;password
                d:filename;password
                filename.typ;password
                d:filename.typ;password


Some CP/M commands accept wildcard (* and ?) characters in the
filename and/or filetype parts of the command tail.  A wildcard
in the command line can in one command reference many  matching
files  on  the  default  or specified user number and drive.
This is sometimes refferred to as an 'afn' or amibiguous
filename.  If no wildcards are present, an 'ufn' or unambiguous
filename results.
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