1. REGISTER TRANSFER LANGUAGE (RTL)
BASIC SYMBOLS

2. Today’s Outline Register Transfer Language Type of Registers
Basic Symbols
Register Transfer
Arithmetic Microoperations

3. Register Transfer Language (RTL)
HIGH LEVEL LANGUAGE
Example : C+, VB, JAVA
ASSEMBLY LANGUAGE
Example : uP and uC
OPCODE
MICROCODE
RTL
to represent registers
specify the operations on their contents
Mircocode (Micro-operations):
Operations executed on data stored in registers, performed in one clock cycle
Register Transfer Language (RTL):
Symbolic notation used to describe micro-operations

4. Register Transfer Language (RTL)
Is an algebraic notation used to define machine level operations
It is not executed by a computer
It is used to explain how the computer works.
Example:
In assembly language instruction
ADD #3, D2
is define in RTL as
[D2] [D2] + 3

5. Types of Registers AR : Address Registers DR: Data Registers
A register holds an address for memory unit
DR: Data Registers
PC : Program Counter
IR : Instruction Register
Rn : n indicates the Register number
e.g. R2 is Register 2

6. Block Diagram of Registers7
8 bit Register 6 5 4 3 2 1
Bit 7
Bit 0 R
Register
Bit 16
Bit 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
8 bit = 1 byte
16 bit Register
PC(H)
PC(L)
H = High order byte
L = Low order byte
PC(H) = PC(15:8)
PC(L) = PC(7:0)

7. BASIC SYMBOLS R followed by a number is referring to a register:
R2 = second register/register no 2 R2

8. BASIC SYMBOLS M refers to Memory with addresses in square braces:
Direct Addressing :
M[10] = contents of memory address 10 9 10 11
Address
Content
MEMORY
In this example,
M[10] refers to

9. BASIC SYMBOLS
In-direct Addressing : M[R3] = content of the memory address in R3 15 16 17
Address
Content
MEMORY 1 2 3
REGISTER
= 15
Ans : M[R3] refers to

10. BASIC SYMBOLS Arrow pointing to the right shows transfer of data :
R4 R3 = Stores the value of R3 into R4
Destination Source
The word transfer is misleading, since it implies that data is moved from one location to another. In fact, the data is copied from one location to another since it also still resides in register R3
=> Contents of the source REG do not change,
Only change the contents of destination REG

11. BASIC SYMBOLS A comma represents simultaneous transfer: R1 R2, R6 R7
 Stores R2 into R1 and at the same time stores R7 into R6.

12. BASIC SYMBOLS A colon indicates the termination of function: K: R1 R2
If K=1, then stores R2 into R1.
K1K2’: R3 R2
If K=1 and K2=0, then stores R2 into R3.
K: a control signal generated in the control unit, 0 or 1

13. BASIC SYMBOLS Parenthesis (bracket) indicates part of the register.
R8(1) = bit 1of R8
LSB : Least Significant Bit
MSB : Most Significant Bit R8 7 6 5 3 4 2 1
Bit Position
Content
MSB
LSB

14. BASIC SYMBOLS Parenthesis indicates part of the register.
R3(7:0) = the least significant byte of R3 R3 7 6 5 3 4 2 1
14..9 15 8
0..1
Note : 1 byte = 8 bit

15. Summary Symbol Description Example Square brackets
Specifies an address for memory
M[R2]
Capital Letters & Numerals
Denotes a register
AR, IR, PC, R2
Parentheses
Denotes part of a register
R2(1), R2(7:0), PC(L)
Arrow
Denotes Transfer of data
R1 R2
Colon
Denotes termination of control function K:
Comma
Separates simultaneous transfers
R1 R2, R3 R2

16. 10 minutes break…

17. ARITHMETIC MICROOPERATIONS
The basic arithmetic microoperations are
Addition
Subtraction
Increment
Decrement
The additional arithmetic microoperations are
Add with carry
Subtract with borrow
Transfer/Load
etc. …

18. MATHEMATICAL AND LOGICAL SYMBOLS
Addition is indicated by the + sign:
R1 R2+R3
Add R2 and R3, stores in R1
R2 R4+R1
Add R4 and R1, stores in R2
Example 1 :
Example 2 :

19. MATHEMATICAL AND LOGICAL SYMBOLS
Subtraction is handled not with the minus sign but with complementing.
1’s complement :
2’s complement :
R3 minus R4 in 1’s complement
R5 R3+R4
R3 minus R4 in 2’s complement
R5 R3+R4+1
Note : Computers use the 2’s complement for negative integer numbers in all arithmetic operations.

20. ARITHMETIC MICROOPERATIONS
+ Addition
- Subtraction
* Multiplication
/ Division
Example: R2 R1+R2
Example: R2 R1+R2’+1
Example: R2 R1*R2
Example: R2 R1/R2

21. ARITHMETIC MICROOPERATIONS
Summary of Typical Arithmetic Microoperations
(Page 547)
Note : Any register may be specified for source 1, source 2, or destination.

22. REGISTER TRANSFER LANGUAGE
REGISTER TRANSFERS
A little bit revision…

23. Microoperations
MICROOPERATIONS
Microoperations - The operations performed on data stored in registers or in memory.
The functions built into registers are examples of microoperations
Shift
Load
Clear
Increment …

24. Microoperations
MICROOPERATIONS
The microoperations most often encountered in digital systems are of four types:
Register transfer microoperations
Transfer binary data from one REG to another
Arithmetic microoperations
Perform arithmetic on data in REG
Logic microoperations
Perform bit manipulation on data in REG
Shift microoperations
Shift data in REG

25. Register Transfer
REGISTER TRANSFER
Copying the contents of one register to another is a register transfer.
A register transfer is indicated as
R2  R1
In this case the contents of register R1 are copied (loaded) into register R2.
A simultaneous transfer of all bits from the source R1 to the destination register R2, during one clock pulse.
Note that this is a non-destructive; i.e. the contents of R1 are not altered by copying (loading) them to R2

26. REGISTER TRANSFER R3  R5 A register transfer such as
Implies that the digital system has
the data lines from the source register (R5) to the destination register (R3)
Parallel load in the destination register (R3)
All bits are loaded simultaneously on clock pulse (same source)
Control lines to perform the action
Control the transfer or clock cycles

27. CONDITIONAL REGISTER TRANSFER
Conditional Statement
Using control signal to control the transfer
Can be symbolized by if-then statement
if (K1 = 1) then (R2 R1)
In RTL we can write it as:
K1 : R2 R1
The transfer operation be executed only if K1=1
K1: control signal
A subscripted letter followed by a colon is a conditional

28. CONDITIONAL REGISTER TRANSFER
K1 : R2 R1 R2 R1 K1
CLK n
Load control input
n = no of lines = no of bits
Transfer occurs in parallel
Transfer occurs here
CLK K1

29. CONDITIONAL REGISTER TRANSFER
Example:
K1 :R5 R2
Content of R2 will be stored in R5 when condition K1 occurs R5 K1 R2

30. SIMULTANEOUS OPERATIONS
Register Transfer
SIMULTANEOUS OPERATIONS
If two or more operations are to occur simultaneously, they are separated with commas
K: R3  R5, AR  IR
If the control function K = 1, load the contents of R5 into R3, and at the same time (positive clock edge), load the contents of register IR into register AR

31. COMPLEX LOGICAL SYMBOLS
Register Transfer
COMPLEX LOGICAL SYMBOLS
Content of R5 will be stored in R4 only IF
both condition K1 and condition K2 are true:
K1K2:R4 R5
If K1=1 and K2=1, then stores R5 into R4

32. COMPLEX LOGICAL SYMBOLS
Register Transfer
COMPLEX LOGICAL SYMBOLS
Content of R5 will be stored in R4 IF
either condition K1 or condition K2 were
true, a + sign would be used:
(K1+K2) : R R5
NOTE:
In (K1 + K2), “+” means “OR”
In R1 ← R1 + R3, “+” means “plus”

33. COMPLEX LOGICAL SYMBOLS
Register Transfer
COMPLEX LOGICAL SYMBOLS
If – then – else is implemented with commas and multiple colons.
If K1 true, then stores R4 into R6, else if K2 true, then stores R5 into R6, else store R7 into R6.
K1 : R6 R4, K1K2 : R6 R5, K1K2: R6 R7