Question: How can I use a common EEPROM to configure two HX3 hubs?
Answer:
HX3 supports the standard I2C protocol to configure it from an external EEPROM. Multiple HX3 hubs (I2C master mode) can share a common EEPROM. In this case, the image is loaded one at a time for each HX3. See Figure 1.
Figure 1. HX3 Hubs in Master Mode Accessing a Slave I2C EEPROM
When the first HX3 hub is accessing the EEPROM, the I2C Master Arbitration protocol detects that the bus is busy. The second HX3 hub waits until the first HX3 hub completes downloading the image. After the image is downloaded successfully by the first HX3 hub, the second HX3 hub starts accessing the I2C EEPROM.
The sequential accessing by the two HX3 hubs is achieved by de-asserting the reset pins with a delay between the first and second HX3 hubs. Reset de-assertion delay can be controlled by an RC circuit. Cypress recommends approximately 400-ms delay for reset de-assertion to ensure that the image is completely downloaded to the first HX3 hub from the EEPROM. See Figure 2.
Figure 2. Recommended Delay for Deasserting Reset
Note: Both HX3 hubs read configurations from the same address and therefore read the same configuration. If you require different configurations for each hub, you should use separate EEPROMs.