register transfer language (rtl) basic symbols. today’s outline register transfer language ◦...

REGISTER TRANSFER REGISTER TRANSFER LANGUAGE (RTL)LANGUAGE (RTL)BASIC SYMBOLS

Today’s OutlineToday’s OutlineRegister Transfer Language

◦Type of Registers◦Basic Symbols◦Register Transfer◦Arithmetic Microoperations

HIGH LEVEL LANGUAGEExample : C+, VB, JAVA

ASSEMBLY LANGUAGEExample : uP and uC

OPCODE

MICROCODE

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

Register Transfer Register Transfer Language (RTL)Language (RTL)

RTL• to represent registers• specify the operations on their contents

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 68000 assembly language instruction ADD #3, D2

is define in RTL as [D2] [D2] + 3

Register Transfer LanguageRegister Transfer Language(RTL)(RTL)

Types of RegistersTypes of RegistersAR : Address Registers

◦A register holds an address for memory unit

DR: Data RegistersPC : Program CounterIR : Instruction RegisterRn : n indicates the Register

number◦e.g. R2 is Register 2

Block Diagram of Block Diagram of RegistersRegisters

R

PC(H)

Register

16 bit Register

7

8 bit Register

6 5 4 3 2 1 0

Bit 7 Bit 0

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Bit 16 Bit 0

PC(L)

8 bit = 1 byte

H = High order byte L = Low order byte

PC(H) = PC(15:8) PC(L) = PC(7:0)

BASIC SYMBOLSBASIC SYMBOLS

R followed by a number is referring to a register:

R2 = second register/register no 2

R2

BASIC SYMBOLSBASIC SYMBOLS M refers to Memory with

addresses in square braces:

Direct Addressing : M[10] = contents of memory address

10

In this example, M[10] refers to 10111011

100000001011101111111111

91011

Address Content

MEMORY

BASIC SYMBOLSBASIC SYMBOLSIn-direct Addressing :M[R3] = content of the memory

address in R3

100000001011101111111111

151617

Address Content

MEMORY

100000000000011000001111

123

Address Content

REGISTER

00001111= 15

Ans : M[R3] refers to 10000000


Arrow pointing to the right shows transfer of data :

R4 R3 = Stores the value of R3 into R4

• 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

Destination Source

BASIC SYMBOLSBASIC SYMBOLS A comma represents simultaneous transfer:

R1 R2, R6 R7

Stores R2 into R1 and at the same time stores R7 into R6.

BASIC SYMBOLSBASIC SYMBOLS A colon indicates the termination of function:

K: R1 R2If K=1, then stores R2 into R1.

K1K2’: R3 R2If K=1 and K2=0, then stores R2

into R3.K: a control signal generated in the control unit, 0 or 1


Parenthesis (bracket) indicates part of the register.

R8(1) = bit 1of R8

R8

7 6 5 34 2 1 0

1 0 1 11 0 0 0

Bit Position

Content

MSB LSB

LSB : Least Significant BitMSB : Most Significant Bit


Parenthesis indicates part of the register.

R3(7:0) = the least significant byte of R3

Note : 1 byte = 8 bit

R3

7 6 5 34 2 1 0

1 0 1 11 0 0 0

14..915 8

10..1

SummarySummarySymbol 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

10 minutes break…

ARITHMETIC ARITHMETIC MICROOPERATIONSMICROOPERATIONSThe basic arithmetic

microoperations are◦Addition◦Subtraction◦Increment◦Decrement

The additional arithmetic microoperations are◦Add with carry◦Subtract with borrow◦Transfer/Load◦etc. …

Arithmetic Microoperations

MATHEMATICAL AND LOGICAL MATHEMATICAL AND LOGICAL SYMBOLSSYMBOLS Addition is indicated by the +

sign:

R1 R2+R3Add R2 and R3, stores in R1

R2 R4+R1Add R4 and R1, stores in R2

Example 1 :

Example 2 :

MATHEMATICAL AND LOGICAL MATHEMATICAL AND LOGICAL SYMBOLSSYMBOLSSubtraction is handled not with

the minus sign but with complementing.

1’s complement :

2’s complement :

R5 R3+R4

R5R3+R4+1

Note : Computers use the 2’s complement for negative integer numbers in all arithmetic operations.

+ Addition

- Subtraction

* Multiplication

/ Division

Example: R2 R1+R2

Example: R2 R1+R2’+1

Example: R2 R1*R2

Example: R2 R1/R2

ARITHMETIC ARITHMETIC MICROOPERATIONSMICROOPERATIONS

Summary of Typical Arithmetic Microoperations(Page 547)

Arithmetic Microoperations

ARITHMETIC ARITHMETIC MICROOPERATIONSMICROOPERATIONS

Note : Any register may be specified for source 1, source 2, or destination.

REGISTER TRANSFER REGISTER TRANSFER LANGUAGELANGUAGEREGISTER TRANSFERS

A little bit revision…A little bit revision…

MICROOPERATIONSMICROOPERATIONS

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◦…

Microoperations

MICROOPERATIONSMICROOPERATIONSThe 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

Microoperations

REGISTER TRANSFERREGISTER 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

Register Transfer

REGISTER TRANSFERREGISTER TRANSFER

A register transfer such as

R3 R5

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

Register Transfer

CONDITIONAL REGISTER TRANSFERCONDITIONAL 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

A subscripted letter followed by a colon is a conditional

Register Transfer

K1: control signal


R2R1

K1

CLK

n

K1

CLK

Transfer occurs here

n = no of lines = no of bits

Transfer occurs in parallel

K1 : R2 R1

Register Transfer

Load control input

K1 :R5 R2


Content of R2 will be stored in R5 when condition K1 occurs

R5

R2

K1

Example:

Register Transfer

SIMULTANEOUS OPERATIONSSIMULTANEOUS 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

Register Transfer

COMPLEX LOGICAL SYMBOLSCOMPLEX LOGICAL SYMBOLS

Content of R5 will be stored in R4 only IF both condition K1 and condition K2 are true:

K1K2:R4 R5

Register Transfer

If K1=1 and K2=1, then stores R5 into R4


Content of R5 will be stored in R4 IFeither condition K1 or condition K2 weretrue, a + sign would be used:

(K1+K2) : R4 R5

NOTE: In (K1 + K2), “+” means “OR” In R1 ← R1 + R3, “+” means “plus”

Register Transfer


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

Register Transfer

1

O R 2

register transfer language (rtl) basic symbols. today’s outline register transfer language ◦...

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