Read and Write EEPROM Using SPI Blocks on Renesas RH850 Microcontrollers

Prerequisites

Before you begin,

Required Hardware

EEPROM Module Concepts

Memory Layout and Addressing

The 25XX080 has 8 KBits (1024 bytes) requiring 10 address bits (A0–A9).

The memory is divided into 16-byte pages. Writes must not cross page boundaries in a single operation. When writing multiple bytes (for example, the address increments past 0bxxxx 1111), the internal address counter rolls over to the start of the same page, overwriting previous data. To write to contiguous memory across page boundaries, for each page, increment the address by 0x10 (16 decimal) and then perform a write operation.

This table, from the Microchip 25XX080 8K SPI Bus Serial EEPROM datasheet, shows the module instruction set.

Write to EEPROM

To write to the EEPROM:

1. Set the write enable latch with the WREN instruction by completing this write enable sequence:

Drive chip select (CS) line low > Send 0x06 > Drive CS line high

If you do not set the write enable latch (WEL) or toggle the CS line, a silent failure occurs.

2. Initiate a write operation with the WRITE instruction by completing this page write sequence:

Drive CS line low > Send 0x02 (WRITE) > Send 16-bit Address > Send Data (Max 16 bytes) > Drive CS line high after data byte is transferred

3. Trigger a write cycle.

To write data to memory, drive the CS line high after the least significant bit (D0) of the last data byte has been clocked in. Otherwise, the write operation does not complete.

The Microchip 25XX080 8K SPI Bus Serial EEPROM datasheet mentions that the internal write cycle time (Twc) is a maximum of 5 ms and an attempt to read from a memory location is not possible during a write cycle.

The write enable latch (WEL) is automatically reset when the write cycle is completed.

Read from EEPROM

Initiate a data read from an address of the EEPROM after confirming that data was successfully written. You have two options for checking the status of a write operation:

To poll the WIP bit:

To read from the EEPROM, initiate this sequence of operations:

The address pointer automatically increments, allowing the entire array to be read in a single sequence,

Set Up Hardware Connections

Hardware connections depend on whether you use the EEPROM in your application. In this example, the Renesas RH850 board (acting as SPI controller) connects to a 25AA080 SPI EEPROM chip using MSPI0.

Read and Write EEPROM Data Using SPI Controller Transfer Block

Open the RH850spiEEPROM.slx Simulink model.

modelName = "RH850spiEEPROM";
open_system(modelName) 

The model is pre-configured for Renesas RH850 U2A Based hardware.

Ensure the following settings are applied:

The model contains two main subsystems:

Model Overview

The example model (RH850spiEEPROM) demonstrates both write and read operations with the 25AA080 EEPROM using a single Simulink model. The model uses the MCAL SPI block configured for synchronous transmission.

EEPROM Write Subsystem

This subsystem contains two SPI blocks executed in priority order. WREN must always be Priority 1 because the WEL bit is required by the EEPROM before it will accept a WRITE command.

SPI Transfer Execution Order

Note: The EEPROM automatically clears the Write Enable Latch (WEL) after each successful write operation. Therefore, the WREN command (0x06) must be sent before every WRITE operation. Sending WREN only during initialization can cause subsequent write operations to be ignored.

EEPROM Read Subsystem

The SPI EEPROM Read subsystem executes when a change in the write address or write data generates a rising-edge trigger. The subsystem reads data from the EEPROM using the configured SPI read sequence and returns the received data for display and verification.

Received Data Handling

The SPI receive buffer contains both transmitted and received information. The instruction byte and address bytes returned by the EEPROM are discarded, while the received EEPROM data bytes are forwarded to the display block for comparison with the transmitted data.

Monitor and Tune the Model on Hardware

In the Simulink model, click Hardware tab and then click Monitor & Tune.This deploys the model to the target hardware.

Observe the displayed values for:

If the configuration is correct, the read-back data should match the values written to the EEPROM.

Results

When the model runs: