The document discusses different types of control flow in computer programs including sequential, selection, iteration, and recursion. It explains that in a control flow computer, instructions are executed sequentially based on the program counter. Shared memory is used to pass data between instructions by reference. Control flow computers perform computations synchronously using centralized control.

1. By- Rudra Prasad Saha

2.  In computer science , control flow (or
alternatively, flow of control) refers to the order
in which the
individual statements,instructions, or function
calls of an imperative or
a declarative program are executed or
evaluated.
 Within an imperative programming
language, a control flow statement is a
statement whose execution results in a choice
being made as to which of two or more paths
should be followed. For non-strict functional
languages, functions and language constructs
exist to achieve the same result, but they are
not necessarily called control flow statements.

3.  Instruction execution in a conventional
computer is under program-flow control.
 Data is passed between instructions via
references to shared memory cells.
 Flow of control is implicitly sequential, but
special control operators can be used
explicitly for parallelism.
 Program counter (PC) register is used to
sequence the execution of instructions in a
centralized control environment.
 Synchronous Computations are performed
in control flow computers using centralized
control.

4. Microprogram
- Program stored in memory that generates all the control
signals required to execute the instruction set correctly
- Consists of microinstructions
Basic Elements of Processor
•ALU
•Registers
•Internal data paths
•External data paths
•Control Unit

6. •Program Counter (PC)
Holds address of next instruction to be fetched
•Memory Address Register (MAR)
Connected to address bus
Specifies address for read or write op
•Memory Buffer Register (MBR)
Connected to data bus
Holds data to write or last data read
•Instruction Register (IR)
Holds last instruction fetched

7. •Address of next instruction is in PC
•Address (MAR) is placed on address bus
t1: MAR  (PC)
•Control unit issues READ command
•Result (data from memory) appears on
data bus
•Data from data bus copied into MBR
t2: MBR  (memory)
•PC incremented by 1 (in parallel with data
fetch from memory)
PC  (PC) +1 Fetch cycle
•Data (instruction) moved from MBR to IR
t3: IR  (MBR)
•MBR is now free for further data fetches

8. 1) THE SYSTEMATIZATION OF CONTROL
2) IMPROVEMENT IN PERFORMANCE
a) a high degree of parallelism in data paths e.g., multiple bit
microinstructions are
performed in one cycle
b) a high degree of decision logic (in table search and sorting routines)
3) COMPUTER-SERIES COMPATIBILITY
Compatibility of instruction sets between smaller and larger machines of a
series,
e.g., Intel286, 386, Pentium, IBM Systems/309x, Motorola 68000 series
4)Software support
Eases programing

9.  State the task to be performed.
 Devise a register-transfer description of the
algorithm based on the processing section.
 Establish the design of the processing section by
providing necessary control signals.
 Provide a block diagram of the controller section.
 Generate the state diagram of the controller
section with different control state.
 Specify the characteristics of the hardware
components to be used in the controller section.
 Give the complete design of the controller and
draw a logic diagram of the final circuit.

10.  DATAPATH- perform
data transfer and Control signals
processing operation.
Status signals
 Control Unit -
Control Control
Datapath
inputs
Determines the
enabling and Data
sequencing of the Control Data outputs
operations
outputs inputs
 The control unit receive
the control inputs &
generate control signals.

13.  Sequential – Execution of prog. statement as per
sequence.
 Selection – A run-time choice of what to execute
next depending on condition.
 Iteration – Repeating execution of a block of
statements.
 Recursion –Repeatedly calling of a function or
set of statements until no further call.

14.  When one
statement occurs
before another in
the program, the
first statement
executes before
the second,i.e as
they appear on
program.  Fig:sequential flow control

15. If there be any
condition on
execution of a
sequence of
statements, in a
program then the
control flows
depending on the
selection of the part
to be executed.
Fig: select max among 3 no(s)

16. When some block of
statements get
executed continuously
till the value of the
Loop Counter satisfies a
given condition which
controls the no of
repetition to be done, is
called Iteration.
Also known as Iterative
Loop or simply Loop.

17. If in a program a
function is defined
as such, so that it
will call itself until
further call does not
satisfy the condition
of recursive calling.
The function is
called Recursive
function.

18. • In the control flow
program representations
the statement a= (b+1) *
(b - c) is specified by a
series of instructions
with an explicit flow of
control.

19. • Shared memory cells are the means by which data
is passed between instructions. Data (operands)
are referenced by their memory addresses
(variables).
• In the traditional sequential control flow model
(von Neumann) , there is a single thread of
control which is passed from instructions to
instructions.
• In control flow execution of instruction depends
upon flow of control. But in data flow architecture
instruction execution depends on availability of
data token.