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# 1.40 TWIHS EEPROM Emulation

This example application demonstrates how to use the TWIHS peripheral in client mode.

## Description

This example uses the TWIHS peripheral library in client mode and emulates an EEPROM of 512 bytes. There are two pages each of size 256 bytes. TWIHS client expects two bytes of memory address from the TWIHS host and the memory address can range from 0x00 to 0x1FF. TWIHS client application supports following:

Byte Write: The TWIHS host sends the client address, followed by two bytes of memory address. The client provides the data present at the requested memory address.

Page Write: A page write is initiated the same way as a byte write, but the TWIHS host can write up-to 256 bytes (1 page). If more than 256 bytes are sent by the TWIHS host to the TWIHS client, the memory address will “roll over” and previous data will be overwritten. The address “roll over” during write is from the last byte of the current page to the first byte of the same page.

Current Address Read: The internal memory address counter maintains the last address accessed during the last read or write operation, incremented by one. Once the device address with the read/write bit set to one is clocked in and acknowledged by the EEPROM, the data byte at the current address is serially clocked out. After reading the data from the current address, the TWIHS host sends NAK and generates a STOP condition.

Random Read: The TWIHS host writes the 2 byte memory address and then reads the data from that memory address. After reading the data, the TWIHS host sends NAK and generates a STOP condition.

Sequential Read: Sequential reads are initiated by either a current address read or a random address read. As long as the EEPROM receives an acknowledge, it will continue to increment the memory address and serially clock out sequential data bytes. When the memory address limit is reached (0x1FF), the memory address will “roll over” to 0x00 and the sequential read will continue. The sequential read operation is terminated when the TWIHS host sends a NAK and generates a STOP condition.

To run the application, two evaluation kits will be required - one acting as the TWIHS host and the other as the TWIHS client. The TWIHS host application to be used for this demo application is available under apps/twihs/master/twihs_eeprom/firmware folder. TWIHS host writes an array of values to the TWIHS client and verifies the value written by reading the values back and comparing it to the value written.

## Downloading and Building the Application

To clone or download this application from Github, go to the main page of this repository and then click Clone button to clone this repository or download as zip file. This content can also be downloaded using content manager by following these instructions.

Path of the application within the repository is apps/twihs/slave/twihs_eeprom_emulation/firmware.

To build the application, refer to the following table and open the project using its IDE.

Project Name | Description
--- | ---
sam_e70_xult.X | MPLABX project for SAM E70 Xplained Ultra Evaluation Kit

## Setting Up the Hardware

The following table shows the target hardware for the application projects.

Project Name | Description
--- | ---
sam_e70_xult.X | SAM E70 Xplained Ultra Evaluation Kit

Hardware setup requires two boards, one acting as the TWIHS Host and the other as the TWIHS client.

### Setting Up SAM E70 Xplained Ultra Evaluation Kit

- On EXT1 header, connect TWIHS SDA line on Pin 11 (PA03) and TWIHS SCL line on Pin 12 (PA04) with the corresponding SDA and SCL lines of the TWIHS host
- Connect a ground wire between TWIHS host and TWIHS client boards
- Connect the Debug USB port on the board to the computer using a micro USB cable

## Running the Application

1. Open the twihs_eeprom application from apps/twihs/master/twihs_eeprom/firmware and open the main.c file. Make sure the following macro is defined to false.

       #define I2C_SLAVE_IS_ONBOARD_EEPROM           false

2. Build and program TWIHS EEPROM application from apps/twihs/master/twihs_eeprom/firmware onto the evaluation kit used as TWIHS host
3. Build and Program TWIHS client application onto the evaluation kit used as TWIHS client
4. Run application on TWIHS client board and then run the application on TWIHS host board
5. LED on the TWIHS host board indicates success or failure:
   - The LED is turned ON when the value read from the TWIHS client matches with the written value
   - The LED is turned OFF when the value read from the TWIHS client did not match with the written value