EEPROM Memory: Programming and Interfacing the Microchip 93LC46B-E/MS Serial Chip

Electrically Erasable Programmable Read-Only Memory (EEPROM) is a non-volatile memory technology that allows individual bytes of data to be erased and reprogrammed. It is widely used for storing configuration parameters, calibration data, or small amounts of critical information in embedded systems. Among the many available EEPROM devices, the Microchip 93LC46B-E/MS stands out as a popular and reliable serial EEPROM chip, offering 1K bits (128 x 8 or 64 x 16) of memory in a compact 8-pin MSOP package. Its simple 3-wire serial interface makes it easy to interface with a wide range of microcontrollers.

The 93LC46B communicates via a Microwire-compatible synchronous serial interface, which consists of three essential signals: Chip Select (CS), Serial Clock (SK), and Serial Data Input/Output (DI/DO). This minimal pin count is a significant advantage in space-constrained designs. The device supports a wide voltage range (2.5V to 5.5V) and features both software and hardware write protection mechanisms to prevent accidental data corruption.

Interfacing with a Microcontroller

The process of connecting the 93LC46B to a microcontroller (MCU) is straightforward. The MCU's general-purpose I/O (GPIO) pins are used to emulate the Microwire protocol, as many modern MCUs do not have a dedicated Microwire peripheral. The connections are simple:

The MCU's GPIO pin connects to the EEPROM's CS pin to initiate and terminate a communication session.

A second GPIO pin connects to the SK pin to provide the clock signal that synchronizes data transfer.

A third GPIO pin is configured as an output to send data (DI) to the EEPROM.

A fourth GPIO pin is configured as an input to receive data (DO) from the EEPROM.

Programming and Instruction Set

Programming the 93LC46B involves sending a specific sequence of instructions and data. All communication is initiated by taking the CS pin high. The first byte transmitted is a Start Bit (1) followed by a 2- or 3-bit opcode that defines the operation (Read, Write, Erase, Write Enable, or Write Disable), and then a 6- or 7-bit address (depending on the memory organization mode).

Key Instructions:

EWEN (Erase/Write Enable): This instruction must be issued before any programming (Write or Erase) operation can be performed. It is a critical safety feature.

WRITE: After the opcode and address, the data word (8 or 16 bits) is sent. The EEPROM automatically enters a self-timed programming cycle after receiving the data.

READ: After the opcode and address, the data from the specified memory location is shifted out on the DO pin.

ERASE: This instruction clears the entire memory cell at a specific address to all '1's.

EWDS (Erase/Write Disable): This instruction protects the memory from inadvertent write operations and is recommended at the end of a programming sequence.

A crucial aspect of writing data is polling the device's readiness. After initiating a write cycle, the MCU can toggle the clock and monitor the DO pin. The pin is held low during the internal write cycle and returns high upon completion, signaling that the device is ready for the next command.

ICGOOODFIND

The Microchip 93LC46B-E/MS is an excellent choice for developers seeking a robust, low-pin-count, non-volatile memory solution. Its simple 3-wire interface and comprehensive instruction set make it incredibly easy to integrate into projects using almost any modern microcontroller. The built-in write protection features ensure data integrity, solidifying its role as a fundamental component in countless embedded systems for data storage and device configuration.

Keywords: EEPROM, Serial Interface, Microwire, Non-volatile Memory, Write Protection