A Guide to Interfacing with the Microchip 24LC16B 16-Kbit Serial EEPROM
The Microchip 24LC16B is a 16-Kbit (2048 x 8) serial Electrically Erasable Programmable Read-Only Memory (EEPROM) that serves as a reliable non-volatile storage solution for a vast array of microcontroller-based systems. Its utilization of the I²C (Inter-Integrated Circuit) protocol makes it a popular choice for applications requiring compact, low-power, and simple-to-interface memory. This guide provides a practical overview of connecting and communicating with this versatile chip.
Key Features and Pinout
The 24LC16B is organized as 2048 words of 8 bits each. It features a page write capability of 16 bytes and supports both byte and page write operations. It is designed for low-power operation, making it ideal for battery-powered devices. The standard 8-pin DIP or SOIC package has the following pin configuration:
A0, A1, A2: These are not connected for device addressing on the 24LC16B. They must be connected to VSS or left floating. Device addressing is handled internally based on memory location.
VSS (Ground): Circuit ground (0V).
SDA (Serial Data): The bidirectional data line for transferring addresses and data. This line requires an external pull-up resistor.
SCL (Serial Clock): The clock input line, which is used to synchronize data transfer. This line also requires an external pull-up resistor.
WP (Write Protect): When connected to VCC, this pin activates hardware write protection, preventing any write operations to the entire memory array. When connected to VSS, write operations are allowed.
VCC: The supply voltage pin (ranges from 1.7V to 5.5V).
The I²C Communication Protocol
The 24LC16B operates as a slave device on the I²C bus. Communication is initiated by a master device, typically a microcontroller. The I²C protocol is characterized by:
A Start Condition: A high-to-low transition on the SDA line while SCL is high.
A Stop Condition: A low-to-high transition on the SDA line while SCL is high.
Data validity: Data on the SDA line must be stable during the high period of the SCL clock pulse. Changes can only occur when SCL is low.
Device Addressing
Following a Start condition, the master must output a Control Byte. For the 24LC16B, this byte is structured as follows:
[ 1 | 0 | 1 | 0 | A10 | A9 | A8 | R/W‾ ]
The first four bits (1010) are the device identifier. The next three bits (A10, A9, A8) are the most significant bits of the memory address, effectively selecting one of eight 256-byte blocks within the memory. The final bit (R/W‾) specifies the operation: '1' for a read operation and '0' for a write operation.
Writing Data
A write sequence involves two key operations:
1. Byte Write: The master sends the Start condition, the Control Byte (with R/W‾=0), the 8-bit memory address (A7-A0) within the selected block, and then the data byte to be written. The sequence is terminated by a Stop condition.
2. Page Write: The master can write up to 16 bytes in a single sequence. After sending the Control Byte and the starting memory address, the master can transmit up to 16 consecutive data bytes. The internal address pointer auto-increments after each byte. Exceeding the 16-byte page boundary will cause the address to "wrap around" and overwrite data from the start of the page.
After receiving each acknowledge bit, the chip enters an internally timed write cycle (tWR), typically lasting up to 5ms. During this time, the device will not respond to its slave address.
Reading Data
Read operations are more flexible:
1. Current Address Read: The chip internally maintains an address pointer that increments after each operation. The master can simply send a Start condition and a Control Byte (with R/W‾=1) to read from this last used address + 1.
2. Random Read: To read from a specific address, the master first performs a dummy write operation. It sends the Control Byte (R/W‾=0) and the desired address. Then, it sends a Repeated Start condition, followed by the Control Byte with R/W‾=1, and receives the data byte.
3. Sequential Read: After initiating a read (either Current or Random), the master can continue to read sequential addresses by providing acknowledge bits after each received byte. The internal address pointer will automatically increment until the master issues a No Acknowledge followed by a Stop condition.
Hardware Interfacing
A typical connection circuit between a microcontroller and the 24LC16B is straightforward. The SDA and SCL lines must each be connected to VCC via a pull-up resistor (typically between 4.7kΩ and 10kΩ, depending on bus speed and capacitance). The VCC and VSS pins are connected to the power supply. The A0-A2 and WP pins can be tied to VSS if not used.
ICGOOODFIND: The Microchip 24LC16B serial EEPROM remains a cornerstone for embedded design, offering a perfect blend of simple I²C interfacing, low-power operation, and reliable non-volatile storage in a minimal footprint, making it an excellent choice for countless applications.
Keywords:
1. I²C Protocol
2. Serial EEPROM
3. Non-volatile Memory
4. Device Addressing
5. Page Write
