OT:I2C chips

Archiver

Do the SDA and SCL pins on I2C chipc always get pulled high?

Thanks

Sid


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Archiver

Yes, that is part of the I2C specification. Devices on the I2C bus are
only allowed to pull the lines low (high is created by the pull-ups).
This way if two devices talk at the same time there will not be short,
just garbled data.

-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office

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Original Message

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Subject: [noparse][[/noparse]basicstamps] OT:I2C chips


Do the SDA and SCL pins on I2C chipc always get pulled high?

Thanks

Sid

Archiver

>Do the SDA and SCL pins on I2C chipc always get pulled high?
>
>Thanks
>
>Sid

Sid,

The sda line definitely needs to have a pullup so that each side,
master and slave, can pull it low.

In a Stamp based system using I2C, the Stamp will always be the buss
master and it will supply the clock signal. So if you are
bit-banking I2C, you can have the Stamp use PULSEOUT or SHIFT
commands to generate the clock, and you don't have to turn it into an
input, nor do you have to supply a pullup resistor on SCL. It is
still best to supply a pullup, because the Stamp pins are inputs by
default at reset.

If you use the I2CIN and I2COUT commands on the BS2p and BS2pe, you
have to supply pullup resistors for both sda and scl, because the
Stamp asserts only the low level and expects the resistor to be there
for the high on both of the pins.

-- Tracy