5 ms max for 24LC and 24C – 10 ms max for 24AA 24C ( 24xx*) is a 32K x 8 (K bit) Serial Elec- CMOS Serial EEPROM. I2C is a . Adding External I2C EEPROM to Arduino (24LC). This tutorial was originally posted on the website, which now seems to be no longer with us. Buy low price, high quality 24c eeprom with worldwide shipping on

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The WP pin stands for write-protected and this allows you to control if data can be written to the eeprom or not. To illustrate this lets follow the steps below. After our data and power pins 24v256 connected we have four left on 24LC chip, the WP pin and the three address pins.

24C Technical Data

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See the address of the device below. For more details Please refer to the Datasheet below. Below is the entire tutorial code, scan over it and see if you understand it before I dive into what each section does. Click to learn more. The 24C is optimized for use in minimal storage applications where low-power and low-voltage operation, driven using i2C serial communication bus to help you do much more multiple series of storage.

The first argument is the address of the device you want to write to, in our case we only have one device disk1 so we pass this on. This means our 24LC chip gets the address and then which tells it to store the next byte in address location 20, Next we have to send the address on the eeprom we want to write to. Check out our videos Follow us on: Before we get into the software part lets hook up the 24LC chip up to our Arduino.


Working on 24C256 EEPROM 256Kbit / 32 Kbyte Serial Memory Data Storage on i2C Bus

Finally we have to pass along the byte we want to store. Time to move on to software! The first send function takes the eeaddress and shifts the bits to the right by eight which moves the higher end of the 16 bit address down to the lower eight bits.

The next three bits A2,A1,A0 are the important bits that we can change so lets look at the simple table below to see what address the chip will have depending on what we set these pins to.

We first call the Wire. Lets say we want to write to address location 20, which is in binary.

Adding External I2C EEPROM to Arduino (24LC256)

The 24LC gets the data and writes the data to that address location. Next lets go ahead and connect the data pins to the Arduino board. This is written for Arduino versions before 1. For more information please read http: This allows the chip time to complete the write operation, without this if you try to do sequential writes weird things might happen. We need to send the MSB Most significant bits first so we have to shift our address to the right eight bits.

The Wire library allows you to pass an integer value so we could just make a bit-wise operation to device the integer variable into two bytes.

For the purpose of explaining how the address works we can ignore the Start and Acknowledge bits.


Next we start off just like we did with ee;rom write function by starting the process with beginTransmission and then we send the address we want to access; this works exactly the same way as the write function.

The following code allows you to write all the bytes of memory. As you can see the diagram above the pin A0, A1, A2 are connected to the ground these pins allow you to customize the device i2C deprom address, below the data sheet we that we verify eeprmo it is formed the byte address.

The next function requestFrom sends the command to that chip to start sending the data at the address we set above. This variable is not required but it allows us to easily change the address we want to access without going through all of the code and replacing the value.

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Adding External I2C EEPROM to Arduino (24LC)

Next we do a bitwise AND to get just the last eight bits. The arguments it accepts are the same first two arguments the write function, the device address and the address on the eeprom to read from.

Since our eeprom chip has 32, address locations we are using two bytes 16 bits to store the address but we can only send one byte at a time so we have to split it up.

This is a little confusing at first so lets look at the figure below to explain the address in a little more detail.