Embedded System

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Compiled By : Richa Arora Akshat Rohtagi ECE HMRITM

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The embedded system is a combination of computer hardware, software additional electrical & mechanical parts A computer is used in such devices primarily as a means to simplify the system design and to provide flexibility. Embedded systems employ the use of a RTOS (Real-Time Operating System).

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Block Diagram of Embedded System

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Microcontroller RAM ROM I/O Port Timer Serial COM Port CPU A smaller computer. On-chip RAM, ROM, I/O ports... Example:- Motorola’s 6811, Intel’s 8051 and PIC 16X A single chip Microcontroller

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IC 8051 MICROCONTROLLER

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The 8051 Microcontroller : The 8051 is the first microcontroller of the MCS-51 family introduced by Intel Corporation at the end of the 1970’s. The 8051 family characteristics: ○ The 8051 family characteristics: ○ 4K Bytes ROM ○ 128 Bytes RAM ○ two timer/counters (16 bit) ○ A serial port ○ 32 input/output port ○ Interrupt controller

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8051 Internal Architecture

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IC 8051 Pin Description Ground Voltage Supply (+5V)

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IC 8051 Pin Description Port 0 from Pin-39 to Pin-32 An 8-bit open drain bidirectional port. DUAL FUNCTION Used to access both data and address

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IC 8051 Pin Description Port 1 from Pin-1 to pin-8 8-bit bidirectional I/O port with internal pull-ups

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IC 8051 Pin Description Port 2 from Pin-21 to pin-28 Used to access address and I/O

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IC 8051 Pin Description Port 3 from Pin-10 to Pin-17 P3.0 : RxD(serial input port) P3.1 :TxD (serial output port) P3.2 : INT0 (external interrupt 0) P3.3 : INT1 (external interrupt 1) P3.4 :T0 (timer 0 external input) P3.5 :T1 (timer 1 external input) P3.6 :WR (external data memory write strobe) P3.7 :RD (external data memory read strobe)

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crystal reset External memory Add. Latch enable Program Store Enable IC 8051 Pin Description

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IC 8051 Daily Applications Moving message display Digital clock Traffic Light 7 segment display

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Immediate addressing modes ADD A, #23h (Add immediate data to Acc) Register addressing modes ADD A, R2 (Add register to Accumulator) Direct addressing modes ADD A, 40h (Add data at location 40h to Accumulator) Register Indirect addressing modes ADD A,@R2 (Add indirect RAM to Acc) IC 8051 Addressing Modes

Interrupts in 8051:

Interrupts in 8051 An interrupt is an external or internal event that interrupts the microcontroller to inform it that a device needs its service The advantage of interrupts is that the microcontroller can serve many devices (not all at the same time) time Interrupt service Program Program

Interrupts in 8051:

Interrupts in 8051 EA - ET2 ES ET1 EX1 ET0 EX0 Internal Interrupts EX0 Enables or disables external interrupt ET0 Enables or disables timer 0 overflow interrupt EX1 Enables or disables external interrupt 1 ET1 Enables or disables timer 1 overflow interrupt ES Enables or disables the serial port interrupt ET2 Enables or disables timer 2 overflow or capture interrupt -- Not implemented, reserved for future use EA Disables all interrupts External Interrupts P3.2 :INT0 (external interrupt 0) P3.3 :INT1 (external interrupt 1)

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CPU General-Purpose Micro-processor RAM ROM I/O Port Timer Serial COM Port Data Bus Address Bus General-Purpose Microprocessor System CPU for Computers No RAM, ROM, I/O on CPU chip itself Example--Intel’s x86: 8086,8088,80386,80486, Pentium Many chips on mother board General Purpose Microprocessor

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IC 8085 MICROPROCESSOR

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The 8085 Microprocessor : The features of INTEL 8085 are : It is an 8 bit processor. It is a single chip N-MOS device with 40 pins. It has multiplexed address and data bus.(AD0-AD7). It works on 5 Volt dc power supply. The maximum clock frequency is 3 MHz while minimum frequency is 500kHz. It provides 74 instructions with 5 different addressing modes.

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IC 8085 Pin Description

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AD0-AD7: Multiplexed Address and data lines. A8-A15: Tri-stated higher order address lines. ALE: Address latch enable is an output signal.It goes high when operation is started by processor . S0,S1: These are the status signals used to indicate type of operation. RD¯: Read is active low input signal used to read data from I/O device or memory. WR¯: Write is an active low output signal used write data on memory or an I/O device. IC 8085 Pin Description

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READY: This an output signal used to check the status of output device.If it is low, µP will WAIT until it is high. TRAP: It is an Edge triggered highest priority , non mask able interrupt. After TRAP, restart occurs and execution starts from address 0024H. RST 5.5,6.5,7.5: These are maskable interrupts and have low priority than TRAP. INTR¯&INTA: INTR is a interrupt request signal after which µP generates INTA or interrupt acknowledge signal. IO/M¯: This is output pin or signal used to indicate whether 8085 is working in I/O mode(IO/M¯=1) or Memory mode(IO/M¯=0 ). IC 8085 Pin Description

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HOLD&HLDA: HOLD is an input signal .When µP receives HOLD signal it completes current machine cycle and stops executing next instruction. In response to HOLD µP generates HLDA that is HOLD Acknowledge signal. RESET IN¯: This is input signal. When RESET IN¯ is low µp restarts and starts executing from location 0000H. SID: Serial input data is input pin used to accept serial 1 bit data . X1 & X2 : These are clock input signals and are connected to external LC,or RC circuit.These are divide by two so if 6 MHz is connected to X1X2, the operating frequency becomes 3 MHz. VCC & VSS: Power supply VCC=+ -5Volt& VSS=-GND reference. IC 8085 Pin Description

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8085 Internal Architecture

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Accumulator: It is 8 bit general purpose register. It is connected to ALU. So most of the operations are done in Acc. Temporary register: All the arithmetic and logical operations are done in the temporary register but user can’t access it. Flag: It is a group of 5 flip flops used to know status of various operations done. The Flag Register along with Accumulator is called PSW or Program Status Word. Arithmetic and Logical Group

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S: Sign flag is set when result of an operation is negative. Z : Zero flag is set when result of an operation is 0. Ac : Auxiliary carry flag is set when there is a carry out of lower nibble or lower four bits of the operation. CY: Carry flag is set when there is carry generated by an operation. P: Parity flag is set when result contains even number of 1’s. Rest are don’t care flip flops. Arithmetic and Logical Group S Z - AC - P - CY Flag is given by :

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Temporary registers (W,Z): These are not available for user. These are loaded only when there is an operation being performed. General purpose: There are six general purpose registers in 8085 namely B,C,D,E,H,L These are used for various data manipulations. Special purpose : There are two special purpose registers in 8085: SP : ( Stack Pointer) This is a temporary storage memory 16 bit register. Since there are only 6 general purpose registers, there is a need to reuse them PC: ( Program Counter) It is 16 bit register used to point the location from which the next instruction is to be fetched. Register Group

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Immediate addressing: Immediate data is transferred to address or register. Example : MVI A,20H Register addressing: Data is transferred from one register to other. Example : MOV A, C Indirect addressing: Data is transferred from address pointed by the data in a register to other register or vice-versa. Example: MOV A, M Implied addressing: These doesn’t require any operand. The data is specified in Opcode itself. Example: RAL: Rotate left with carry. IC 8085 Addressing modes

Interrupts in 8085:

Interrupts in 8085 An interrupt is considered to be an emergency signal that may be serviced. The Microprocessor may respond to it as soon as possible. Interrupts can also be classified into: Maskable Interrupts (Can be delayed or Rejected) Non-Maskable Interrupts (Can not be delayed or Rejected) The 8085 has 5 interrupt inputs. The INTR input : INTR is mask-able using the EI/DI instruction pair. RST 5.5, RST 6.5, RST 7.5 : They are all mask-able. TRAP : is the only non-mask-able interrupt in the 8085

Interrupts in 8085:

Interrupts in 8085 The 8085 recognizes 8 RESTART instructions: RST0 - RST7 . Each of these would send the execution to a predetermined hard-wired memory location: Restart Instruction Equivalent to RST0 CALL 0000H RST1 CALL 0008H RST2 CALL 0010H RST3 CALL 0018H RST4 CALL 0020H RST5 CALL 0028H RST6 CALL 0030H RST7 CALL 0038H

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The µP operates with reference to clock signal. The rise and fall of the pulse of the clock gives one clock cycle. Each clock cycle is called a T state and a collection of several T states gives a machine cycle. Important machine cycles are : Op-code fetch. Memory read. Memory write. I/Op-read. I/O write. Timing and State Diagram

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Timing and State Diagram Op-code fetch cycle :

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Seven segments are electronic components that can be used to displaying alphanumeric characters, 7 LED are used (as shown in figure) and is designed from a dot-point with the size. pin configuration of seven segment Seven Segment Display

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Port Relations Microcontroller with pin 7 Segment 7 pins of the microcontroller are used to shape the character of your LED display Seven Segment Display

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Table 1. Configuring the Character 7 Segment Data Seven Segment Display

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8051 Microcontroller Design Softwares

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Software’s Used Keil µVision Top View Simulator Express PCB

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Keil µVision IDE The µVision IDE from Keil combines project management, make facilities, source code editing, program debugging, and complete simulation in one powerful environment. The µVision development platform is easy-to-use and helping you quickly create embedded programs that work. The µVision editor and debugger are integrated in a single application that provides a seamless embedded project development environment.

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Top View Simulator Topview Simulator gives an excellent simulation environment for MCS 51 Microcontroller. A beginner can learn about 8051 based embedded solutions without any hardware. An experienced designer, you may find most of the required facilities built in the simulator that enabling  you to complete your next project without waiting for the target hardware.

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Top View Simulator A Top View Simulator Program

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Express PCB Express PCB allows you to design schematics and PCB's. It is ideal for those that are looking to design anywhere from a two to four layer circuit board. A drop and drag design allows users to pick the components of the circuit board and drop it onto the circuit board in the software program. The designer can then place various pins in the circuit board to show where things need to be connected. It also has the ability of the program to show the designer where there are flaws in their design.

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This way we can include resistors This way we can include different kind of IC’s Express PCB

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DC Motor interfacing with Microcontrollers DC motors are always preffered over stepper motors. There are many things which we can do with our DC motor when interfaced with microcontroller. For example: we can control the speed of motor, we can control the direction of rotation, we can also do encoding of the rotation made by DC motor i.e. keeping track of how many turns are made by our motors etc. Usually H-bridge is preffered way of interfacing a DC motor. L293D is most used H-Bridge driver IC.

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Working of H-Bridge The name "H-Bridge" is derived from the actual shape of the switching circuit which control the motion of the motor. It is also known as "Full Bridge". Basically there are four switching elements in the H-Bridge as shown

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Truth Table For H-Bridge Truth Table High Left High Right Low Left Low Right Description On Off Off On Motor runs clockwise Off On On Off Motor runs anti-clockwise On On Off Off Motor stops or decelerates Off Off On On Motor stops or decelerates

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Stepper Motor Of all motors, step motor is the easiest to control. It's handling simplicity is really hard to deny - all there is to do is to bring the sequence of rectangle impulses to one input of step controller and direction information to another input. Direction information is very simple and comes down to "left" for logical one on that pin and "right" for logical zero. Motor control  is also very simple - every impulse makes the motor operating for one step and if there is no impulse the motor won't start. Pause between impulses can be shorter or longer and it defines revolution rate. This rate cannot be infinite because the motor won't be able to "catch up" with all the impulses (documentation on specific motor should contain such information)..

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Interfacing of Stepper motor with 8051

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Clock-wise Rotation of the Coils 1 2 3 4 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 Truth table