Unit 2.2 -- One more example--Handling a constant

PROG

Add A to B and then subtract one, putting the result into C

PED

To learn how to represent constants

CONCEPTS

Use

label   DC  f'nn'

to put a constant in a memory location at load time.

SF


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                            Unit 2.2
                            English

Unit 2.2 performs the operation C:=A+B-1.

Notice  the  presence of the constant,  -1,  in  the  PASCAL
statement.   The constant can be stored using the  DC  f'nn'
instruction  we  learned about earlier.  The  name  of  this
memory  location  is F1.  It signifies the  "F"  in  the  DC
command followed by M for "Minus" and then 1.  We could  use
any  name for our constant such as "SUGAR" or "BLAH"   There
is no magic to the namin convention I am using.

This is done at line 16--memory location 000032.

Since this is only the second ASSEMBLER  program,  you  have
been  formally  shown,  I will describe  the  steps  in  the
execution once again.

The program executes as follows.

There  are now four boxes.  A, B and FM1 are initialized  to
3,4  and  -1,  respectively.  These values are  loaded  into
memory  as  the  program itself, including the instructions,
are put into memory.

The  "L  1,A"  copies the 3 in the A box  to  register  one.
Register one now will be three.

The  "A  1,B"  adds  the  4 in the B box  to  register  one.
Register one will now be seven.

The  "A  1,FM1"  adds the -1 in the C box to  register  one.
Register one will now be six.

The "ST 1,C" copies the six in register one  to  the  memory
location.  C is now six.