SPRZ398K November 2012 – September 2024 DRA745 , DRA746 , DRA750 , DRA756
I2C Module in Multislave Mode Potentially Acknowledges Wrong Address
Low
When the I2C module is in multislave mode with up to four 10-bit own addresses it may acknowledge the wrong address. According to the I2C protocol, a 10-bit address is sent via 2 bytes. The first byte is formatted as 11110XX R/W where XX are the 2 MSB of the address. The second byte contains the remaining 8 bits of the device address.
When the first byte received contains 2 MSB that matches the 2 MSB of the one of the modules four own addresses, an ACK is correctly sent by the module. However, if the second byte received matches the remaining 8 bits of one of the modules other own addresses, an ACK is sent incorrectly by that module. In turn, the incorrect module then enters an internal state where starts reading data sent on the bus not intended for it.
The module should only send a second ACK if the entire 10-bit address matches one of its four own addresses. However, the module incorrectly ACKs any address that matches the first 2 bits of one slave address and the last eight bits of another slave address.
The issue can be avoided by ensuring that the 2 most significant bits are identical for all multislave addresses in 10-bit addressing mode.
SR 2.0, 1.1, 1.0
TDA2x: 2.0, 1.1, 1.0
DRA75x, DRA74x: 2.0, 1.1, 1.0
AM572x: 2.0, 1.1