Implementing LBRDISK with ZCPR2

     ZCPR2  checks  the drive code when attempting to log into  a 
new  disk.   Since LBRDISK is often used to create psuedo  drives 
higher  than the installed drive,  it is necessary to change  the 
MAXDISK equate in ZCPRHDR.LIB.  Besides, it is the responsibility 
of the BIOS to check for (and gracefully recover from) an invalid 
physical disk selection.  

     I  suggest  setting MAXDISK to 15 and  re-installing  ZCPR2.  
Oh,  and it is a good idea to set MAXUSER to 15 for compatibility 
with CP/M+ and other CP/M systems.

     If  you have the source code for your BIOS the beginning  of 
the SELDSK routine should be something like the following:

     SELDSK:   MOV  A,C       ;Get new disk
               LXI  H,0       ;Flag possible invalid disk
               CPI  MAXDSK    ;or whatever the variable name for
                              ;maximum physical drive is.
               JC   DSKOK     ;Jump if ok
               XRA  A
               STA  4         ;So that the CCP is not caught in
                              ;a loop
               RET
     DSKOK:    STA  SEKDSK    ;or whatever the variable name is
               .
               .
     (Remainder of SELDSK routine)
               .
               .

     If  there is room in your BIOS,  you should install code  to 
print  an  error  message on select error,  and jump  to  WBOOTE.  
Note:   it  must jump to WBOOTE,  not to WBOOT so  that  the  RSX 
manager can intercept.


Jim Lopushinsky
March 7/84
403-484-5981  @ 300/1200 baud.