SYLLABUS

AERONAUTICAL ENGINEERING

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AUTOMOBILE ENGINEERING

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BIOMEDICAL ENGINEERING

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CIVIL ENGINEERING

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CSE

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EIE

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IT

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MECHATRONICS ENGINEERING

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MECHANICAL ENGINEERING

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Servo Motor

 What are Servo Motors?

Servo refers to an error sensing feedback control which is used to correct the performance of a system. Servo or RC Servo Motors are DC motors equipped with a servo mechanism for precise control of angular position. The RC servo motors usually have a rotation limit from 90° to 180°. Some servos also have rotation limit of 360° or more. But servos do not rotate continually. Their rotation is restricted in between the fixed angles.

Where are Servos used?

The Servo motors are used for precision positioning. They are used in robotic arms and legs, sensor scanners and in RC toys like RC helicopter, airplanes and cars
ervo Motor manufacturers

There are four major manufacturers of servo motors: Futaba, Hitec, Airtronics and JR radios. Futaba and Hitec servos have nowadays dominated the market. Their servos are same except some interfacing differences like the wire colors, connector type, spline etc.

Servo Motor Manufacturers

Servo Motor wiring and plugs
The Servo Motors come with three wires or leads. Two of these wires are to provide ground and positive supply to the servo DC motor. The third wire is for the control signal. These wires of a servo motor are color coded. The red wire is the DC supply lead and must be connected to a DC voltage supply in the range of 4.8 V to 6V. The black wire is to provide ground. The color for the third wire (to provide control signal) varies for different manufacturers. It can be yellow (in case of Hitec), white (in case of Futaba), brown etc.

Futaba provides a J-type plug with an extra flange for proper connection of the servo. Hitec has an S-type connector. A Futaba connector can be used with a Hitec servo by clipping of the extra flange. Also a Hitec connector can be used with a Futaba servo just by filing off the extra width so that it fits in well.

Hitec splines have 24 teeth while Futaba splines are of 25 teeth. Therefore splines made for one servo type cannot be used with another. Spline is the place where a servo arm is connected. It is analogous to the shaft of a common DC motor.

Structure of Servo Motor


Unlike DC motors, reversing the ground and positive supply connections does not change the direction (of rotation) of a servo. This may, in fact, damage the servo motor. That is why it is important to properly account for the order of wires in a servo motor.

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What is the difference between a DC motor and servo motor?

A DC motor has a two wire connection. All drive power is supplied over these two wires—think of a light bulb. When you turn on a DC motor, it just starts spinning round and round. Most DC motors are pretty fast, about 5000 RPM (revolutions per minute).

With the DC motor, its speed (or more accurately, its power level) is controlled using a technique named pulse width modulation, or simply PWM. This is idea of controlling the motor’s power level by strobing the power on and off. The key concept here is duty cycle—the percentage of “on time” versus“off time.” If the power is on only 1/2 of the time, the motor runs with 1/2 the power of its full-on operation.

If you switch the power on and off fast enough, then it just seems like the motor is running weaker—there’s no stuttering. This is what PWM means when referring to DC motors. The Handy Board’s DC motor power drive circuits simply switch on and off, and the motor runs more slowly because it’s only receiving power for 25%, 50%, or some other fractional percentage of the time.

A servo motor is an entirely different story. The servo motor is actually an assembly of four things: a normal DC motor, a gear reduction unit, a position-sensing device (usually a potentiometer—a volume control knob), and a control circuit.

The function of the servo is to receive a control signal that represents a desired output position of the servo shaft, and apply power to its DC motor until its shaft turns to that position. It uses the position-sensing device to determine the rotational position of the shaft, so it knows which way the motor must turn to move the shaft to the commanded position. The shaft typically does not rotate freely round and round like a DC motor, but rather can only turn 200 degrees or so back and forth.

The servo has a 3 wire connection: power, ground, and control. The power source must be constantly applied; the servo has its own drive electronics that draw current from the power lead to drive the motor.

The control signal is pulse width modulated (PWM), but here the duration of the positive-going pulse determines the position of the servo shaft. For instance, a 1.520 millisecond pulse is the center position for a Futaba S148 servo. A longer pulse makes the servo turn to a clockwise-from-center position, and a shorter pulse makes the servo turn to a counter-clockwise-from-center position.

The servo control pulse is repeated every 20 milliseconds. In essence, every 20 milliseconds you are telling the servo, “go here.”

To recap, there are two important differences between the control pulse of the servo motor versus the DC motor. First, on the servo motor, duty cycle (on-time vs. off-time) has no meaning whatsoever—all that matters is the absolute duration of the positive-going pulse, which corresponds to a commanded output position of the servo shaft. Second, the servo has its own power electronics, so very little power flows over the control signal. All power is draw from its power lead, which must be simply hooked up to a high-current source of 5 volts.

Contrast this to the DC motor. On the Handy Board, there are specific motor driver circuits for four DC motors. Remember, a DC motor is like a light bulb; it has no electronics of its own and it requires a large amount of drive current to be supplied to it. This is the function of the L293D chips on the Handy Board, to act as large current switches for operating DC motors.

Plans and software drivers are given to operate two servo motors from the HB. This is done simply by taking spare digital outputs, which are used to generate the precise timing waveform that the servo uses as a control input. Very little current flows over these servo control signals, because the servo has its own internal drive electronics for running its built-in motors.

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Applications of Microcontroller

The reason I find microcontrollers fascinating is that they have been and continue to be such an important part of the electronics industry.  Over the past decade and more microcontrollers have been creeping into our daily lives.  Figure 1 shows how microcontrollers increased in popularity from 1991 through 1996.

In today’s world, microcontrollers are used in just about every electronic object in the household and place of business.  Just about the only common object in the house that does not have a microcontroller in it is the light bulb.  In fifteen years or so even that may not be the case.

The reason microcontrollers have become so common is that they are more than merely reliable.  By adding a small computer to many devices it is possible to increase efficiency or safety, or any number of other features.

Timing devices are now composed almost entirely of microcontrollers.  This has made them unbelievably accurate.  They are also cheap, and much more reliable.  A digital watch today, which has no moving parts, is almost impossible to break through normal use.  It is easy to adapt digital watches to extreme environments such as the deep sea or vacuum.

Telephones and other personal communication devices also use microcontrollers. With such devices it is possible to have wireless telephones and cellular phones, each capable of maintaining a connection between the phone unit and some sort of base station.  These phones can also encrypt data as it leaves and decrypt it as it comes in.

Televisions and stereos use microcontrollers.  Neither is the mess of tubes that was synonymous with televisions and radios.  As a result, both produce better quality picture and sound, have more features, and weigh less per unit volume.

All kinds of transportation systems use microcontrollers.  Cars use them in fuel injection systems, brakes, airbags, and just about any other piece of equipment.

Airplanes are going to a “fly-by-wire” control system.  This is a complex computer interface between the controls that the pilot uses and the control surfaces of the plane. Such interfaces are controlled by microcontrollers.

Modern traffic lights are controlled by microcontrollers.  Emergency phones by the highways of America have solar panels, batteries, and a microcontroller circuit to operate in remote areas. 

            Microcontroller's use increased rapidly. Now these are used in almost every electronic equipment like Washing Machines, Mobile Phones and Microwave Oven. Following are the most important facts about Microcontrollers, which causes rapid growth of their use:

Microcontrollers are cheap and very small in size, therefore they can be embedded on any device.

Programming of Microcontrollers is simple to learn. Its not much complicated.

We can use simulators on Computers to see the practical results of our program. Thus we can work on a Embedded project without even buying the required Components and Chips. Thus we can virtually see the working of our project or program.

Microcontrollers are mostly used in following electronic equipments :

• Mobile Phones
• Auto Mobiles
• CD/DVD Players
• Washing Machines
• Cameras
• In Computers-> Modems and Keyboard Controllers
• Security Alarms
• Electronic Measurement Instruments.
• Microwave Oven

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ARCHITECTURE OF 8051

Each block will be discussed step by step:

 ALU — Arithmetic Logical Unit
This unit is used for the arithmetic calculations.

 A-Accumulator
This register is used for arithmetic operations. This is also bit addressable and 8 bit register.

 B-Register
This register is used in only two instructions MUL AB and DIV AB. This is also bit addressable and 8 bit register.

PC-Program Counter
• Points to the address of next instruction to be executed from ROM
• It is 16 bit register means the 8051 can access program address from 0000H to FFFFH. A total of 64KB of code. 16 bit register means. Initial value 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 (0000H)
Final value 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 (F F F F H)
• Initially PC has 0000H
• ORG instruction is used to initialize the PC ORG 0000H means PC initialize by 0000H

• PC is incremented after each instruction.

Example:

Mnemonics Machine codes

MOV R5, #25H 7D 25

MOV A, #00H 74 00

ADD A, R5 2D

HERE: SJMP HERE; 80 FE

• When 7D is accessed then PC locate the 0001H (next instruction to be executed)

• When 00 is accessed then PC locate the 0004H (next instruction to be executed)

 ROM Memory Map in 8051

→ 4KB, 8KB, 16KB, 32KB, 64KB on chip ROM is available.

→ Max ROM space is 64 KB because 16 bit address line is available in 8051.

→ Starting address for ROM is 0000H (because PC which points the ROM is 16 bit wide).

 8051 Flag Bits and PSW Register

→ Used to indicate the Arithmetic condition of ACC.

→ Flag register in 8051 is called as program status word (PSW). This special function register PSW is also bit addressable and 8 bit wide means each bit can be set or reset independently.

There are four flags in 8051

• P → Parity flag → PSW 0.0

1 – odd number of 1 in ACC

0 – even number of 1 in ACC

• OV(PSW 0.2) → overflow flag → this is used to detect error in signed

arithmetic operation. This is similar to carry flag but difference is only that

carry flag is used for unsigned operation.

• RS1(PSW0.4) RS0(PSW0.3) Register Bank Select

0                              0                            Bank 0

0                              1                            Bank 1

1                              0                            Bank 2

1                              1                            Bank 3

for selecting Bank 1, we use following commands

SETB PSW0.3 (means RS0=1)

CLR PSW0.4 (means RS1=0)

Initially by default always Bank 0 is selected.

• F0 → user definable bit

• AC → Auxiliary carry flag → when carry is generated from D3 to D4, it

is set to 1, it is used in BCD arithmetic.

Since carry is generated from D3 to D4, so AC is set.

•CY → carry flag → Affected after 8 bit addition and subtraction. It is used to detect error in unsigned arithmetic opr. We can also use it as single bit  storage.

SETB C → for cy = 1

CLR C → for cy = 0

 Structure of RAM or 8051 Register Bank and Stack

→ 128 byte RAM is available in 8051

→ 128 byte = 2^7B

Address range of RAM is 00H to 7FH.

→ In MC8051, 128 byte visible or user accessible RAM is available which is shown in figure. Extra 128B RAM which is not user accessible. 80H to FFH used for storage of SFR (special function register)

→ Four Register Banks

→ There are four register banks, in each register bank there are eight 8 bit register available from R0 to R7

→ By default Bank 0 is selected. For Bank 0, R0 has address 00H

R1 has address 01H

. . . . . . . . . . . . . . . .

 . . . . . . . . . . . . . . . .

R7 has address 07H

For Bank 1, R0 has address 08H

R1 has address 09H

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

R7 has address 0FH

For selecting banks we use RS0 and RS1 bit of PSW.

→ R0 to R7 registers are byte addressable means.

 If we want to set the bit 3 of R0 then we can’t use SETB R0.3  We use MOV R0, #08H;

 For changing single bit we can modify all the other bits of R0.

→ Locations 20H to 2FH is bit addressable RAM means each bit from 00H to FFH in this we can set or reset CF rather than changing whole byte.

→ Locations 30H to 7FH is used as scratch pad means we can use this space for data reading and writing or for data storage.

 Stack in 8051

→ RAM locations from 08H to 1FH can be used as stack. Stack is used to store the data temporarily. Stack is last in first out (LIFO)

→ Stack pointer (SP) →

• 8bit register

• It indicate current RAM address available for stack or it points the top of stack.

• Initially by default at 07H because first location of stack is 08H.

• After each PUSH instruction the SP is incremented by one while in MC after PUSH instruction SP is decremented.

• After each POP instruction the SP is decremented.

Example:

MOV R6,#25H;

MOV R1,#12H;

MOV R4,#OF3H;

PUSH 06H;

PUSH 01H;

POP 04H;

→ if we want to use more than 24byte (08H to 1FH) of stack. We can change SP to point RAM address 30H to 7FH by MOV SP, #XX Any value from 30 to 7FH

Conflicting of Register Banks and Stack

→ We know locations from 08H to 1FH is used as stack and it is also used as register bank.

→ If in the program, we use the Register Bank 1 to 3 and also use the stack then conflicts exist and error can be possible. For removing this situation we use the stack from location 30H to 7FH by shifting SP to 2FH. MOV SP,#2FH;

DPTR

→ Data Pointer in 8051

→ 16 bit register, it is divided into two parts DPH and DPL.

→ DPH for Higher order 8 bits, DPL for lower order 8 bits.

→ DPTR, DPH, DPL these all are SFRs in 8051.

Special Function Register

→ (See Fig.) RAM scratch pad, there is extra 128 byte RAM which is used to store the SFRs

→ Following figure shows special function bit address, all access to the four I/O ports CPU register, interrupt control register, timer/counter, UART, power control are performed through registers between 80H and FFH.

Byte Addressable SFR with byte address

SP – Stack printer – 81H

DPTR – Data pointer 2 bytes

DPL – Low byte – 82H

DPH – High byte – 83H

TMOD – Timer mode control – 89H

TH0 – Timer 0 Higher order bytes – 8CH

TL0 – Timer 0 Low order bytes – 8AH

TH1 – Timer 1 High bytes = 80H

TL1 – Timer 1 Low order byte = 86H

SBUF – Serial data buffer = 99H

PCON – Power control – 87H.

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PIN DIAGRAM OF 8051

Description of each pin is discussed here:
•VCC → 5V supply
• VSS → GND
• XTAL2/XTALI are for oscillator input
• Port 0 – 32 to 39 – AD0/AD7 and P0.0 to P0.7
• Port 1 – 1 to 8 – P1.0 to P1.7
• Port 2 – 21 to 28 – P2.0 to P2.7 and A 8 to A15
• Port 3 – 10 to 17 – P3.0 to P3.7
• P 3.0 – RXD – Serial data input – SBUF
• P 3.1 – TXD – Serial data output – SBUF
• P 3.2 –INT0– External interrupt 0 – TCON 0.1
• P 3.3 –INT1– External interrupt 1 – TCON 0.3
• P 3.4 – T0 – External timer 0 input – TMOD
• P 3.5 – T1 – External timer 1 input – TMOD
• P 3.6 –WR– External memory write cycle – Active LOW
• P 3.7 –RD– External memory read cycle – Active LOW
• RST – for Restarting 8051
• ALE – Address latch enable
1 – Address on AD 0 to AD 7
0 – Data on AD 0 to AD 7
• PSEN – Program store enable

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MICROCONTROLLER 8051 ARCHITECTURE

It is 8-bit microcontroller, means MC 8051 can Read, Write and Process 8 bit data. This is mostly used microcontroller in the robotics, home appliances like mp3 player, washing machines, electronic iron and industries. Mostly used blocks in the architecture of 8051 are as follows:

128 Byte RAM for Data Storage

MC 8051 has 128 byte Random Access memory for data storage. Random access memory is non volatile memory. During execution for storing the data the RAM is used. RAM consists of the register banks, stack for temporary data storage. It also consists of some special function register (SFR) which are used for some specific purpose like timer, input output ports etc. Normally microcontroller has 256 byte RAM in which 128 byte is used for user space which is normally Register banks and stack. But other 128 byte RAM which consists of SFRs. We will discuss the RAM in detail in next section.

Now what is the meaning of 128 byte RAM. What are address range which is provided for data storage. We will discuss here.

We know that 128 byte = 2^7  byte

Since 2^7 bytes so last 7 bits can be changed so total locations are from 00H to 7F H. This procedure of calculating the memory address is called as “memory mapping”. We can save data on memory locations from 00H to 7FH. Means total 128 byte space from 00H to 7FH is provided for data storage.

4KB ROM

• In 8051, 4KB read only memory (ROM) is available for program storage. This is used for permanent data storage. Or the data which is not changed during the processing like the program or algorithm for specific applications.

• This is volatile memory; the data saved in this memory does not disappear after power failure.

• We can interface up to 64KB ROM memory externally if the application is large. These sizes are specified different by their companies.

• Address Range of PC: Address range of PC means program counter (which points the next instruction to be executing) can be moved between these locations or we can save the program from this location to this location.

The address range can be calculated in the same way just like the RAM which is discussed in previous section.

Address range of PC is 0000H to 0FFFH means total 4KB locations are available from 0000H to 0FFFH. At which we can save the program.

Difference between RAM and ROM

• RAM is used for data storage while ROM is used for program storage.

• Data of RAM can be changed during processing while data of ROM can’t be changed during processing.

• We can take an example of calculator. If we want to perform addition of two numbers then we type the two numbers in calculator, this is saved in the RAM, but the Algorithms by which the calculation is performed is saved in the ROM. Data which is given by us to calculator can be changed but the algorithm or program by which calculation is performed can’t be changed.

Timers and Counters

Timer means which can give the delay of particular time between some events. For example on or off the lights after every 2 sec. This delay can be provided through some assembly program but in microcontroller two hardware pins are available for delay generation. These hardware pins can be also used for counting some external events. How much times a number is repeated in the given table is calculated by the counter.

• In MC8051, two timer pins are available T0 and T1, by these timers we can give the delay of particular time if we use these in timer mode.

• We can count external pulses at these pins if we use these pins in counter mode.

• 16 bits timers are available. Means we can generate delay between 0000H to FFFFH.

• Two special function registers are available.

• If we want to load T0 with 16 bit data then we can load separate lower 8 bit in TL0 and higher 8 bit in TH0.

• In the same way for T1.

• TMOD, TCON registers are used for controlling timer operation.

1.4.4 Serial Port

• There are two pins available for serial communication TXD and RXD.

• Normally TXD is used for transmitting serial data which is in SBUF register, RXD is used for receiving the serial data.

• SCON register is used for controlling the operation.

• There are four modes of serial communication which has been discussed in next chapter.

Input Output Ports

• There are four input output ports available P0, P1, P2, P3.

• Each port is 8 bit wide and has special function register P0, P1, P2, P3 which are bit addressable means each bit can be set or reset by the Bit instructions (SETB for high, CLR for low) independently.

• The data at any port which is transmitting or receiving is in these registers.

• The port 0 can perform dual works. It is also used as Lower order address bus (A0 to A7) multiplexed with 8 bit data bus P0.0 to P0.7 is AD0 to AD7 respectively the address bus and data bus is demultiplex by the ALE signal and latch which is further discussed in details.

• Port 2 can be used as I/O port as well as higher order address bus A8 to A15.

• Port 3 also have dual functions it can be worked as I/O as well as each pin of P3 has specific function.

 P3.0 – RXD –  Serial I / P for Asynchronous communication

                Serial O / P for synchronous communication.

P3.1 – TXD – Serial data transmit.

P3.2 – INT0 – External Interrupt 0.

P3.3 – INT1 – External Interrupt 1.

P3.4 – T0 – Clock input for counter 0.

P3.5 – T1 – Clock input for counter 1.

P3.6 – WR – Signal for writing to external memory.

P3.7 – RD – Signal for reading from external memory.

When external memory is interfaced with 8051 then P0 and P2 can’t be worked as I/O port they works as address bus and data bus, otherwise they can be accessed as I/O ports.

Oscillator

• It is used for providing the clock to MC8051 which decides the speed or baud rate of MC.

• We use crystal which frequency vary from 4MHz to 30 MHz, normally we use 11.0592 MHz frequency.

Interrupts

• Interrupts are defined as requests because they can be refused (masked) if they are not used, that is when an interrupt is acknowledged. A special set of events or routines are followed to handle the interrupts. These special routines are known as interrupt handler or interrupt service routines (ISR). These are located at a special location in memory.

• INT0 and INT1 are the pins for external interrupts.

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Introduction to Microcontroller

INTRODUCTION

The microcontroller incorporates all the features that are found in microprocessor. The microcontroller has built in ROM, RAM, Input Output ports, Serial Port, timers, interrupts and clock circuit. A microcontroller is an entire computer manufactured on a single chip. Microcontrollers are usually dedicated devices embedded within an application. For example, microcontrollers are used as engine controllers in automobiles and as exposure and focus controllers in cameras. In order to serve these applications, they have a high concentration of on-chip facilities such as serial ports, parallel input output ports, timers, counters, interrupt control, analog-to-digital converters, random access memory, read only memory, etc. The I/O, memory, and on-chip peripherals of a microcontroller are selected depending on the specifics of the target application. Since microcontrollers are powerful digital processors, the degree of control and programmability they provide significantly enhances the effectiveness of the application. The 8051 is the first microcontroller of the MCS-51 family introduced by Intel Corporation at the end of the 1970s. The 8051 family with its many enhanced members enjoys the largest market share, estimated to be about 40%, among the various microcontroller architectures.

The microcontroller has on chip peripheral devices. In this unit firstly we differentiate microcontroller from microprocessor then we will discuss about Hardware details of 8051 and then introduce the Assembly level language in brief.

MICROCONTROLLERS

•  Microcontroller (MC) may be called computer on chip since it has basic features of microprocessor with internal ROM, RAM, Parallel and serial ports within single chip. Or we can say microprocessor with memory and ports is called as microcontroller. This is widely used in washing machines, vcd player, microwave oven, robotics or in industries.

•  Microcontroller can be classified on the basis of their bits processed like

8bit MC, 16bit MC.

•  8 bit microcontroller, means it can read, write and process 8 bit data.

Ex.  8051 microcontroller. Basically 8 bit specifies the size of data bus. 8 bit microcontroller means 8 bit data can travel on the data bus or we can read, write process 8 bit data.

DIFFERENCE BETWEEN MICROCONTROLLER

AND   MICROPROCESSOR

It is very clear from figure that in microprocessor we have to interface additional circuitry for providing the function of memory and ports, for example we have to interface external RAM for data storage, ROM for program storage, programmable peripheral interface (PPI) 8255 for the Input Output ports, 8253 for timers, USART for serial port. While in the microcontroller RAM, ROM, I/O ports, timers and serial communication ports are in built. Because of this it is called as “system on chip”. So in micro-controller there is no necessity of additional circuitry which is interfaced in the microprocessor because memory and input output ports are inbuilt in the microcontroller. Microcontroller gives the satisfactory performance for small applications. But for large applications the memory requirement is limited because only 64 KB memory is available for program storage. So for large applications we prefer microprocessor than microcontroller due to its high processing speed.

CRITERIA FOR SELECTION OF A MICROCONTROLLER 

IN EMBEDDED SYSTEM

Criteria for selection of  micro controller in any embedded system is as following: 

(a)  Meeting the computing needs of task at hand efficiently and cost effectively

                          •  Speed of operation

•  Packing

•  Power consumption

•  Amount of RAM and ROM on chip

•  No. of I/O pins and timers on chip

•  Cost

(b)  Availability of software development tools such as compiler, assembler and debugger.

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