HP 15c Manual

 Appendix B: Stack Lift and the LAST X Register 211 
 
 
T y  y  y  y 
Z x  x  x  x 
Y 4.0000  53.1301  53.1301  53.1301 
X 3  5.0000  0.0000  7 
Keys: |:               |` 7  
   Stack 
enabled. 
 Stack 
disabled. 
 No stack 
lift. 
Imaginary  X-Register. All  enabling  functions  provide  for  a  zero  to  be 
placed  in  the  imaginary  X-register when  the  next  number  is  keyed  or 
recalled into the display. 
Neutral Operations 
Stack  Lift. Some  operations,  like •,  are  neutral;  that  is,...

212 Appendix B: Stack Lift and the LAST X Register 
 
LAST X Register 
The following operations save x in the LAST X register: 
 
- x H \ k 
+ [ H ] ∆ 
* \ h : 
÷ ] À ; 
a , d p* 
q { r c* 
‘ / N z 
& P[  w 
∕ P\ o j 
! P] @ > 5 through 9 
¤ H[ Y f† 
 
                                                           * Except when used as a matrix function. † f uses the LAST X register in a special way, as described in appendix E.  

 
213 
Appendix C 
Memory Allocation 
The Memory Space 
Storage registers, program lines, and advanced function execution* all draw 
on a common memory space in the HP-15C. The availability of memory for 
a  specific  purpose  depends  on  the  current allocation of  memory,  as  well  as 
on the total memory capacity of the calculator. 
Registers 
Memory  space  in  the  HP-15C  is  allocated  on  the  basis  of registers. This 
space is partitioned into two pools, which strictly define how a register...

214 Appendix C: Memory Allocation 
 
 
Total  allocatable memory: 64  registers,  numbered  R2 through  R65.  
[(dd – 1)  + uu + pp + (matrix  elements)  +  (imaginary  stack)  +  (_ 
and f)] =  64.  For  memory  allocation  and  indirect  addressing,  data 
registers R.0 through R.9 are referred to as R10 through R19.   

 Appendix C: Memory Allocation 215 
 
Memory Status (W) 
To  view  the  current  memory  configuration  of  the  calculator,  press | 
W (memory),  holding W to  retain  the  display.* The  display  will  be 
four numbers, 
dd    uu   pp-b 
where: 
dd = the  number  of  the highest-numbered register  in  the  data  storage 
pool (making the total number of data registers dd + 2 because of R0 
and RI); 
uu = the number of uncommitted registers in the common pool; 
pp = the number of registers containing...

216 Appendix C: Memory Allocation 
 
1. Place dd,  the number  of  the  highest  data  storage  register  you want 
allocated, into  the  display.  1dd65.  The  number  of  registers  in  the 
uncommitted  pool  (and  therefore potentially available  for 
programming) will be (65 – dd). 
2. Press ´ m %. 
There are two ways to review your allocation: 
 Press lm % to recall into the stack the number of the 
highest-allocated data storage register, dd. (Programmable.) 
 Press | W (as explained above) to...

 Appendix C: Memory Allocation 217 
 
When converting registers, note that: 
 You can convert registers from the common pool only if they are 
uncommitted. If, for example, you try to convert registers which 
contain program instructions, you will get an Error 10 (insufficient 
memory). 
 You can convert occupied registers from the data storage pool, 
causing a loss of stored data. An Error 3 results if you try to 
address a lost – that is, nonexistent – register. Therefore, it is 
good practice to...

218 Appendix C: Memory Allocation 
 
Your  very  first  program  instruction  will  commit  R65 (all  seven  bytes)  from 
an  uncommitted  register  to  a  program  register.  Your  eighth  program 
instruction commits  R64, and so on, until the  boundary of the  common pool 
is encountered. Registers from the data storage pool (at power-up, this is R19 
and  below)  are  not  available  for  program  memory  without  reallocating 
registers using m %. 
Two-Byte Program Instructions 
The  following...

 Appendix C: Memory Allocation 219 
 
For _ and f,  allocation  and  deallocation  of  the  required  register 
space  takes  place  automatically.* Memory  is  thereby  allocated  only  for  the 
duration of these operations. 
Space  for  the  imaginary  stack  is  allocated  whenever ´ V, ´ 
}, or | F 8 is pressed. The imaginary stack is deallocated when 
 8 is executed. 
Space  for  matrix  registers  is  not  allocated until  you  dimension  it (using 
m).  Reallocation  takes  place  when  you...

 
220 
Appendix D 
A Detailed Look at _ 
Section  13,  Finding  the  Roots  of  an  Equation,  includes  the  basic 
information  needed  for  the  effective  use  of  the _ algorithm.  This 
appendix  presents  more  advanced,  supplemental  considerations  regarding 
_. 
How _ Works 
You  will  be  able  to  use _ most  effectively  by  having  a  basic 
understanding of how the algorithm works. 
In  the  process  of  searching  for  a  zero  of  the 
specified  function,  the  algorithm  uses  the...