Question:
On the MAX6955 EVKIT, the default write addresses for U1 and U2 are 0xCA and 0xC0, respectively. The EVKIT software addresses U1 and U2 at 0x65 and 0x60. Why is that?
Answer:
Take a look at the EVKIT datasheet, page 5, Tables 1 and 2. Notice that there is a write and read address for each pair of jumper settings. I2C uses a 7-bit slave address and one read/write bit. The slave address allows the master to address a specific slave on the bus, and the master sets the read/write bit to indicate that either a read (1) or write (0) is coming.
For example, take U1's default write address of 0xCA. 0x65 is actually the 7-bit slave address without the read/write bit. Take a look:
0xCA = 1100 1010
0x65 = 1100 101X
Appending a read (1) or write (0) bit to the end of 0x65 will make it either 0xCB (read) or 0xCA (write). The GUI is reporting 7-bit slave addresses, while the EVKIT datasheet shows 8-bit read/write addresses.