MCODE - IS THIS FOR YOU
                             Part 3

References:

A.   DATAFILE V6N6 and V6N4.
B.   DATAFILE V5N4.
C.   HP-41 MCODE for Beginners - Ken Emery.

INTRODUCTION

1.   The previous thrilling installment zzzzzzz..... stated that you would be
able to retrieve the keys and buffers back from the RSU data file using the
functions in part 3, in fact it will be part 4.  The reason for this change is
that a facility to delete key assignments is required and so this part
describes such a capability.

DISCUSSION

2.   The extended functions of the 41 include a CLRKEYS function but the
locatiion of the code, unless it is a CX, is dependent on the position of the
ROM.  In implementing DELKEYS to provide the necessary code I have provided a
more versatile facility which will delete all assignments, global assignments
only and function assignments only.  The use of flags 26 and 27 to indicate the 
users requirement is similar to that in part 1.

                          F26
          Clear                           Set

          Clear Globals only          Clear All     Clear
                                   (equiv. to 
                                     CLRKEYS)                 F27

          Clear Globals only      Clear Functions   Set
                                  only

Flag 26 is automatically set after execution of DELKEYS flag 27 remains as at
execution. 

LISTING

3.   The remarks should help understand the function - remember the ZENROM
does not dis-assemble co-located quad Xeq and Gto's correctly-I have crossed
out the appropriate text.

DELKEYS
     
4.  Set flags 26 and 27 as above and execute DELKEYS.

FAT TABLE

5.   Update the table as follows:

          F001 008
          F010 003
          F011 049

MAINFRAME ROUTINES USED IN PART 2 AND 3

     Page                     Octal Address                      Hex Address

     232                      2-0-1350                           22E8

     Description

     ERRSUB- Performs error check routine on flag 25 and exits to a normal
     function return if set otherwise continues with error processing.

     Entry- Nil
     Uses- C and 1 SR level.
     Exit- F25 set, normal function return.
           F25 clear, continue.

     191                      1-3-0200                           1C80

     MSG105- Enables chip 0, set the message flag and prints the message if the
     printer is in trace mode.

     Entry- Nil
     Uses- A, C, G, N and up to 2 SR levels.
     Exit- Don't care.

     233                      2-0-1373                           22FB

     ERR110- Checks the need for back step due to an error, computes a valid
     line number.  Exits to a normal function return.

     Entry- Nil
     Uses- Don't care.
     Exit- Normal function return.

     14                       1-1-1112                           164A

     XSF- Set a user flag.

     Entry- Reg d in A, mask in B (All zero's except for 1 at the locatiion of
     the selected flag).
     Uses- A, B, C, M  and 1 SR level.
     Exit- Appropriate user flag set.

     59                       0-1-1757                           07EF

     Left shift a message into the LCD from the right.

     Entry- LCD enabled.
     Uses- C.
     Exit- LCD enabled on exit.

     31                       2-3-0360                           2CF0

     Enable the display and clear it.

     Entry- Nil
     Uses- C
     Exit- LCD enabled and clear.

6.   Part 4 will contain RCLBUFF and RCLKEYS.  Please forward a disc for the RSU
image or ZENROM's user register format.  Send a SAE for a reply to any queries.

John Bruce
164N