# Multiple I2C devices on Rx daughtercards **URL:** \ **Category:** GNU Radio\ **Created:** [January 11, 2010, 5:56pm UTC](https://www.ruby-forum.com/t/multiple-i2c-devices-on-rx-daughtercards/181420 "2010-01-11T17:56:06Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![ndorphine](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/0ea827/32.png) [@ndorphine](https://www.ruby-forum.com/u/ndorphine)\ **Post date:** [January 11, 2010, 5:56pm UTC](https://www.ruby-forum.com/t/multiple-i2c-devices-on-rx-daughtercards/181420/1 "2010-01-11T17:56:06Z")
Hi Matt, In reviewing the schematic of the dbsrx daughtercard, I noticed that there are two i2c devices (the EEPROM and the MAX211x receiver chip). In general for the daughtercards, address bit A1 determines side A or side B, and A0 determines if the card is an rx or tx card, and this is hard-coded by the USRP itself. So…if a user has two dbsrx cards in their USRP, I think the EEPROM of the dbsrx on side A would have the same address as the MAX211x on side B, and vice versa. Wouldn’t this be an issue? Of course, I’m guessing there is a logical explanation as to how this is mitigated, as I found several folks in the archives that mention using two dbsrx cards simultaneously. Any insight is appreciated. Also, is there a reason that address bit A2 isn’t used to select different i2c devices on the same card? Thanks much… ---
**Author:** ![ndorphine](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/0ea827/32.png) [@ndorphine](https://www.ruby-forum.com/u/ndorphine)\ **Post date:** [January 11, 2010, 10:23pm UTC](https://www.ruby-forum.com/t/multiple-i2c-devices-on-rx-daughtercards/181420/2 "2010-01-11T22:23:38Z")
On Mon, Jan 11, 2010 at 10:51:09AM -0600, John O. wrote: > Hi Matt, > In reviewing the schematic of the dbsrx daughtercard, I noticed that there > are two i2c devices (the EEPROM and the MAX211x receiver chip). In general > for the daughtercards, address bit A1 determines side A or side B, and A0 > determines if the card is an rx or tx card, and this is hard-coded by the > USRP itself. So…if a user has two dbsrx cards in their USRP, I think the > EEPROM of the dbsrx on side A would have the same address as the MAX211x on > side B, and vice versa. Wouldn’t this be an issue? > Also, is there a reason that address bit A2 isn’t used to select different > i2c devices on the same card? I2C devices have a 7-bit address. Some of them are fixed depending on the device. E.g., on the 24LC024, the top 4-bits are 1010, which is different from the bits hardwired into a low speed A/D, D/A, etc. Take a look at the datasheets. Eric ---
**Author:** ![ndorphine](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/0ea827/32.png) [@ndorphine](https://www.ruby-forum.com/u/ndorphine)\ **Post date:** [January 11, 2010, 11:05pm UTC](https://www.ruby-forum.com/t/multiple-i2c-devices-on-rx-daughtercards/181420/3 "2010-01-11T23:05:12Z")
On Mon, Jan 11, 2010 at 3:04 PM, Eric B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > EEPROM of the dbsrx on side A would have the same address as the MAX211x > > Take a look at the datasheets. Ok…that makes sense. I forgot about the hard-wired top bits. This correlates with the code in db\_dbs\_rx.cc that indicates that its i2c address is either 0x67 or 0x65, depending on which side it is in (along with the fact that the schematic has the A1/AS1 address bit controlled from the USRP). Tthe MAX211x datasheet shows the addresses as 1100xxxx, but the LSB is used to indicate read (1) or write (0), so the \_actual\_address of the chip is 1100xxx \>\> 1, which is 0110xxx (where xxx correlates with A2/A1/A0 coming from the USRP). I2c always makes my head hurt until I remember how it works. Thanks again Eric!