2. AC
Load to AC
Store AC
BUN
BSA
Topics
3. AC stands for “Accumulator”.
It is a register for short term and intermediate storage
of arithmetic and logic data in computer’s CPU(central
processing unit).
In a modern computers, any register can function as an
accumulator.
The operation is performed with memory operand and
content of AC.
AC:
4. This instruction transfers the memory word specified by
effective address to AC.
D2T4: DR M[AR]
D2T5: AC DR
The adder and logic circuit receive information from DR
and transferred to AC.
Load to AC:
5. This instruction stores the content of AC into memory
word specified by the effective address.
Output of AC is applied to bus and data input of memory
is connected to bus, we can execute this instruction with
one micro operation.
D3T4: M[AR] AC
Store AC
6. This instruction transfers the program to the instruction
specified by effective address.
BUN instruction allows the programmer to specify an
instruction out of sequence and we say that the program
branches unconditionally.
This instruction is:
D4T4: PC AR
(effective address from AR is transferred through common
bus to PC)
BUN (branch unconditionally):
7. Stands for “branch and save return address”.
This instruction is useful for branching to a portion of a
program called subroutine. When executed, BSA
instruction stores the address of next instruction in a
sequence into the memory location.
M[AR] PC, PC AR+ 1
BSA
