Serial Communication Basics

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I2C communication Very important

Watchdog Timer

The watchdog timer keeps track of the embedded program execution.

This is a register where some value is to be feed at regular intervals otherwise it will generate a reset .

General purpose computers does not have a watchdog but embedded systems had watchdog which monitors the program execution otherwise reset the program automatically

A COP (computer operating properly) or watchdog timer checks for runaway code execution. In

general, watchdog timers must be turned on once within the first few cycles after reset. Software

must then periodically reset the watchdog during execution.

If processor execution has gone off the track, it is unlikely that the watchdog will be reset reliably. It

is this exact state that needs to be fixed: an indirect jump to an unexpected address could be the

cause. A loop polling for external signals that are never received is also a possible cause.

The watchdog timeout can cause the processor to go to a known state, usually the RESET state, or to

execute an interrupt. The hardware implementation of watchdog timers varies considerably between

different processors. Some watchdog timers can be programmed for different time-out delays.

In C, the sequence to reset the watchdog can be as simple as assigning to a port.

Reg communication protocols in Embedded

Not only for human beings communication is important even for silicon chips the communication is very important

In embedded communication can be divided mainly into 2 parts

1. PC to embedded controller communication

2. Embedded controller to embedded controller communication

Even there is another communication method called ASIC communication which happens internally in the ASIC

So now we will see the first part

1. For outside world to communicate with embedded controller a communication is required for example PC sends a command to switch on a relay based on ambient temperature

For this to happen a communication is required, communication means a set of protocol has to be transmitted from PC to Chip , chip has to understand what PC communicates and then has to take decision

In order chip to understand it must recognise first communication started so START bit is initiated and chip also need to understand that communication is terminated generally humans do by telling BYE in this case STOP bit

and chip also should understand that communication is meant for this chip then chip has address has humans has name

and the actual message

so we can tell that communication can be START ADDRESS MESSAGE STOP

but chip also should verify whether received data is correct as transmitted to avoid miscommunication so PARITY is also required

START ADDRESS MESSAGE PARITY STOP

This can be a basic communication from PC to chip

but to transmit data phsically from one place to another place we need physical medium so Tx, Rx, Gnd are minimum needed

Based on number of communication lines and protocols used

1, RS232 communication

2. RS485 communication

3. I2C Communication

4. SPI Communication

6. LIN Communication

7. CAN communication are mostly popular so please read the above communications througly before attending interview best of all

GOOD COMMUNICATION SKILLS ALONG WITH GOOD KNOWLEDGE ON COMMUNICATION PROTOCOLS FETCH YOU A GOOD JOB

BEST OF LUCK

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First Thing to Know

Embedded System is directly related to the microcontroller. So you should have at least knowledge on one microcontroller (8/16/32 Bit). Presently most of the embedded professionals are prefer to write the code in C language. So you should have a good knowledge on C. Instead of C if you know the some other languages like: - C++, Embedded C, Assembly and ADA, it will put very good impression on Interviewer.

Books to Read>

1. 8051 controller by Mazidi

Practice all the exercises not leaving a single example