Atmega64 pins question. SCL/SDA same as TXD/RDX?

Question

I'm not an Atmega pro by any means whatsoever. In fact, never worked with them. I'm trying to add an external eeprom using i2c interface to a device that uses an Atmega64 controller. From the datasheet, I see that pins 25 and 26 are labeled PD0/PD1 and are the SCL/SDA for i2c. That's fine and dandy. So then I go to the board and start tracing. I see that those go to a rocker switch with some simple circuitry that I haven't had a good look at yet, but I assumed it was something i2c compatible. But then what dawned on me was that this device has two such rockers so I expected to trace the other rocker back to the same two pins (since i2c is a bus that can have multiple slaves). Instead, they traced back to the two adjacent pins 27 and 28 labeled PD2/PD3 and RXD1/TXD1. Well, now that confused me.

I expected that I could add the memory in parallel on the SCL/SDA lines, but does what I now figure that what I discovered either means:

1. SCL/SDA is interchangeable with RXD1/RXD2 or
2. I'm confused on how SCL/SDA works and its not a bus or it can be used as a simple input?

Sadly, I'm not really sure what I'm asking. Can someone shed some light on this? Should I still be able to add the memory to SCL/SDA or probably not?

Thanks.

Steve

Answer 1

Nevermind, I found the answer. Its BOTH a bus and a simple input... either one or the other. In this case, its being used as an input so I can't also use it as a bus. Darn. Oh well.