The **M95256-R** is a specific variant of the M95256 series manufactured by STMicroelectronics. It is a 256-Kbit (32 Kbyte) Serial SPI (Serial Peripheral Interface) EEPROM designed for low-voltage applications. --- ## 1. Technical Specifications The "R" suffix in the part number specifically denotes the voltage range and performance characteristics. | Parameter | Value / Range | | :--- | :--- | | **Memory Size** | 256 Kbit (32,768 x 8 bits) | | **Interface** | SPI (Mode 0 and Mode 3) | | **Operating Voltage ($V_{CC}$)** | 1.8V to 5.5V | | **Max Clock Frequency** | 5 MHz (at 1.8V) to 20 MHz (at 4.5V+) | | **Page Size** | 64 Bytes | | **Write Cycle Time** | 5 ms (Maximum) | | **Operating Temperature** | -40°C to +85°C | --- ## 2. Key Internal Components The electronic architecture of the M95256-R consists of several functional blocks: ### A. Memory Array The 256-Kbit non-volatile memory is organized into **64-byte pages**. This structure allows for efficient block writing, where up to 64 bytes can be written in a single $t_W$ (write time) cycle. ### B. Control Logic & Register * **Instruction Register:** Decodes the 8-bit opcodes sent by the SPI Master (e.g., READ, WRITE, WREN). * **Status Register:** Contains the **WIP** (Write In Progress) bit and **WEL** (Write Enable Latch) bit, as well as Block Protect bits (BP0, BP1) for hardware write protection. ### C. SPI Interface Pins | Pin Name | Description | Function | | :--- | :--- | :--- | | **S (Chip Select)** | Slave Select | Activates the device when held low. | | **D (MOSI)** | Serial Data In | Receives instructions and data. | | **Q (MISO)** | Serial Data Out | Outputs data and status register bits. | | **C (Serial Clock)** | Clock Input | Synchronizes data movement. | | **W (Write Protect)** | Hardware Protection | Prevents writes to the status register and memory. | | **HOLD** | Pause Communication | Suspends SPI communication without resetting the chip. | --- ## 3. Performance Features * **Endurance:** High reliability with **4 million** write cycles. * **Data Retention:** Up to **200 years** at room temperature. * **Low Power Consumption:** * Active Read Current: < 2 mA (at 5 MHz). * Standby Current: < 1 µA (at 1.8V). * **Byte/Page Write:** Supports both single-byte writing and 64-byte page writing. --- ## 4. Part Number Decoding (M95256-RMN6P) STMicroelectronics uses a specific nomenclature for these parts: 1. **M95**: SPI Interface EEPROM family. 2. **256**: Density (256 Kbits). 3. **-R**: Operating voltage range (1.8V to 5.5V). 4. **MN**: Package type (e.g., SO8 - 150 mil width). 5. **6**: Temperature range (-40 to 85°C). 6. **P or G**: Process technology (Lead-free/RoHS).