24lc256 EEPROM

[domwild]

Have bought the 28/28X/40X protoboard and this EEPROM and now need to know if I have to install two 4K7 resistors in positions R5 and R6 on the board. Manual says: " ... may need ...". I have not added anything to this board as it says: " ...add only if no pull-ups are already supplied elsewhere on the i2c bus."

Also, it seems to need 0.5mm wire to connect to the protoboard. Is this the correct size?

Thanks.


 

 

[Dippy]

Well, you've nearly answered your own question Dom.

So, have you got pull-up resistors elsewhere in the i2c (SCL/SDA) bus?

Basically, what its saying is: if you haven't got pullups elsewhere then you'll need them on the board.

Remember with I2C that the SDA and SCL lines will need pull-ups, whether you have one EEPROM or half a dozen of them. BUT you DON'T need pullups at every chip.

 

[inglewoodpete]

On the wire size question: 0.5mm would be the recommended size. Thinner than that could introduce unwanted resistance to the connections while thicker wires can be a bit rigid.

Common sense rather than a micrometer should be used when making connections ;o)

 

[domwild]

Thanks for the replies and sorry about the late thanks.

Have I messed something up as I have not added any pull-ups but pressed the chip in so far??

 

[inglewoodpete]

If there are no pullups the operation can be unpredictable. The connections are high impedance and the voltage on them can 'float' anywhere between ground an Vcc. The specification requires 1 pullup resistor on each lead to ensure that the idle state is 'high'.

If you were adding on an i2c device that already has the pullups on-board, then you would not add more.

Alternatively, if you had several i2c devices 'bussed' to the PICAXE, you would have only 1 pullup per lead.

 

[Dippy]

Just like I said in my previous reply.

 

[inglewoodpete]

Hey you're right ;o)

 

[domwild]

Thanks once again for the help. The proto board does have a table of contents, so I can check if those pull-ups already exist. I may also be able to work out which lines are which and if there are resistors.