Transfer Instructions:  JUMP, CALL, RET, JZ, JCZ
Memory Instructions:    LOAD, STORE, LOADP, STOREP, LIT
ALU Instructions:       COM, XOR, AND, ADD, SHL, SHR, ADDNZ
Register Instructions:  LOADA, STOREA, DUP, DROP, OVER, NOP

The F21 had 27 instructions to the MuP21's 24.  (Only 23 are listed
above, hmm.)  They were renamed:

Code Name  Description                         Forth (with a variable named A) 
  00 else  unconditional jump                  ELSE 
  01 T0    jump if T0-19 is false w/ no drop   DUP  IF 
  02 call  push PC+1 to R, jump                : 
  03 C0    jump if T20 is false                CARRY?  IF 
  06 RET   pop PC from R  (subroutine return)  ; 
  08 @R+   fetch from address in R, increment  R    R@  @  R>  1+  >R 
  09 @A+   fetch from address in A, increment  A    A  @  @  1  A  +! 
  0A #     fetch from PC+1, increment PC       LIT 
  0B @A    fetch from address in A             A  @  @ 
  0C !R+   store to address in R, increment R  R@  !  R>  1+  >R 
  0D !A+   store to address in A, increment A  A  @  !  1  A  +! 
  0F !A    store to address in A               A  @  ! 
  10 com   complement T                        -1  XOR 
  11 2*    left shift T, 0 to T0               2* 
  12 2/    right shift T, T20 to T19           2/ 
  13 +*    add S to T if T0 is true            DUP  1  AND  IF OVER + THEN 
  14 -or   exclusive-or S to T                 XOR 
  15 and   and S to T                          AND 
  17 +     add S to T                          + 
  18 pop   pop R, push to T                    R> 
  19 A     push A to T                         A  @ 
  1A dup   push T to T                         DUP 
  1B over  push S to T                         OVER 
  1C push  pop T, push to R                    >R 
  1D A!    pop T to A                          A  ! 
  1E nop   delay 2ns                           NOP 
  1F drop  pop T                               DROP