CPR Modifications
                        =================

This  file  describes the source code modifications to the  ZCPR2 
CPR program.  Both features have been helpful in their own right.  
The graphics mask option has cleaned up a messy screen with  some 
programs  and  the secure ZCPR2 modification has been helpful  on 
RCPM systems.  Perhaps these ideas can be helpful for others.


                                        John C. Smith
                                        Manlius, NY 
                                        December 4, 1983


                          Graphics Mask
                          -------------

This modification integrates another resident command called GRAF 
into the ZCPR system.   Its purpose is to mask off the eighth bit 
from  all  CONOUT  calls  as  a  selectable  option.    This   is 
accomplished  by complementing the GRAPHICS BYTE which is located 
at 004F.   When this byte is zero,  the eighth bit is masked out, 
otherwise it is not.  This prevents unwanted graphics displays on 
the Kaypro 10 screen.

The changes are described below:

                           ZCPRHDR.LIB
                           -----------

Add the following code after WSAVE:
;
WGRAF     EQU  TRUE ; Make GRAF a wheel oriented command
;
Change the WHEEL equate as follows:
;
WHEEL EQU WERA OR WREN OR WLT OR WGO OR WSAVE OR WGET OR WJUMP
          OR WJUMP OR WDU OR WGRAF
;
Add after IF GETON... ENDIF in CTABLE:
;
          DB   'GRAF'    
          DW   GRAF ; TOGGLE GRAPHICS BYTE
;

                            ZCPR2.ASM
                            ---------

Add the following code immediately ahead of Section 5J,  the  GET 
command:
;Section 5I-1
;Command: GRAF
;Function:  To toggle the GRAPHICS BYTE at 04FH on the Kaypro 10.  
;           This is used to optionally mask out the eighth bit of 
;           the  character in  the CONOUT BIOS routine to prevent 
;           unwanted graphics being displayed.
;Form:    GRAF <cr>
GRAF:     IF   WGRAF
          CALL WHLCHK
          ENDIF
          LDA  04FH
          CMA
          STA  04FH
          JMP  RCPRNL
;

This concludes the modifications.

                          Secure ZCPR2 
                          ------------

It  is possible to modify the ZCPR-2 CCP to be more  amenable  to 
the  security  aspects required for RCPM applications  by  taking 
additional  advantage  of  the WHEEL byte used  by  the  resident 
commands  in  the CCP as well as some of the supplied  utilities.  
This  .DOC  file  desicribes the nature and  effect  of  the  CCP 
modofication.

In an RCPM environment, it is desirable to limit the maximum user 
(and  sometimes,  the  maximum  disk) that can be accessed  by  a 
remote  user.   However,  it  would  be nice  to  keep  the  full 
resident addressing facility to all disk/users for the SYSOP.   I 
have added code to the ZCPR-2 CCP to accomplish this.   This code 
does  increase the size of the CCP by about 34 bytes,  so be sure 
to  take  steps  to limit CCP to 2K  maximum.   The  changes  are 
described below:

                           ZCPRHDR.LIB
                           -----------

The change to this file consists of adding the following code  to 
the "Miscellaneous Equates" section of this file as follows:

MAXUSR    EQU  31   ;MAXIMUM USER NUMBER ACCESSABLE
MAXDISK   EQU  3    ;MAXIMUM NUMBER OF DISKS ACCESSABLE
;
;add the following code
;
if        wheel     ;if wheel facility is enabled...
limusr    equ  5    ;max user number with wheel byte reset
limdisk   equ  2    ;max number of disks with wheel byte reset
endif
;
;end of addition
;
SYSFLG    EQU  'S'  ;etc.

In  the  above listing,  the normal capability to to go from  A0: 
through  C31:  with the WHEEL byte set and from A0:  through  B5: 
with the WHEEL byte reset.

                            ZCPR2.ASM
                            ---------


The following code is added to Section 4, ZCPR2 Utilities:

;
;    SET DISK NUMBER (A=1)
;
          SUI  'A'-1     ;CONVERT DRIVE NUMBER TO 1-16
;
;added code
;
          if   wheel     ;wheel byte enabled?
          push psw       ;save disk number
          lda  whladr    ;get wheel byte
          ora  a         ;is it set?
          jrnz jcs1      ;go to jcs1 if it is...
          pop  psw       ;if not, get the disk number
          cpi  limdisk+1 ;is it within range?
          jnc  error     ;invalid disk number
jcs1:     pop  psw       ;get the disk number
          endif
;
;end of added code
;
          CPI  MAXDISK+1 ;WITHIN RANGE?

 More code addition...

;
;    SET USER NUMBER
;
SUD1:     PUSH H         ;(comments deleted)
          XCHG
          CALL NUM0A
          XCHG
          POP  H
;
;added code
;
          if   wheel
          push psw       ;save user number
          lda  whladr    ;get wheel byte
          ora  a         ;is it set?
          jrnz jcs3      ;go to jcs3, if it is
          pop  psw       ;if not, get the user number
          cpi  limusr+1  ;within range?
          jnc  error     ;invalid user number
jcs3:     pop  psw       ;get the user number
          endif
;
;end of added code
;
          IF   USERON    ;etc.

The  above  code  modification has been used on  the  Kaypro  10, 
running ZCPR2 and no problems have been noted.   It is  currently 
in use on the Tampa Bay Bandit Board.  I would appreciate hearing 
of  any problems with this modification.

                    John C. Smith
                    Manlius, NY
                    December 4, 1983