Which I2C address is best used after %10100000?

wapo54001

Senior Member
I have a need for a 20X2 master to communicate with two 28X2 chips with I2C.

I gather that %10100000 is the preferred address to use for a Picaxe slave; is there a preferred address to use for a second Picaxe slave on the same I2C bus?

Are there any gotchas to take into account when consecutively addressing two slave Picaxe chips from a master? The routine will be for the master to send two bytes of data to one slave, then send another two bytes to the second slave, then read two bytes from the first slave followed by reading two bytes of data from the second slave. This needs to happen as quickly as possible without losing reliability. I will be using I2C slow.
 

westaust55

Moderator
There is no mandatory or best i2c slave address for PICAXE parts.

NXP (previously Philips) maintain a list of all "registered" i2c parts with respect to slave address.

The address %1010 xxxy are assigned to memory parts -whereby is the read/write bit.

Since PICAXE as slave parts are usually being written to the scratchpad is is reasonable that Rev Ed suggest %10100000 as a slave address. Therefore is you have a second slave PICAXE part just change one of the lower bits to a 1.
E.g. %10101000 or %10100100 or %10100010.

There are no "gotcha's" with consecutive slave addresses to my knowledge.
 

inglewoodpete

Senior Member
I have used up to 37 PICAXEs in an i2c network, with no other devices like clock or EEPROM chips, and had no problems with i2c addressing of the PICAXE slaves. Each slave had a 6-bit DIP switch and the slaves could have any address between 1 and 63 (formatted as 2 to 126 when the address is shifted one bit to the left).
 
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