SX Micro - 3.3 Volt bus Implementation ?
Murat
Posts: 3
Hi,
My problem is about I2C Bus voltage levels on SX48.
Our I2C bus perepheral is requires bus line (SDA and SCL)·logic high level voltage·up to 3.3 volt.
How can I convert·or implement·SX48 port logic high levels down to 3.3 volt?
Thanks for your help!
Murat
My problem is about I2C Bus voltage levels on SX48.
Our I2C bus perepheral is requires bus line (SDA and SCL)·logic high level voltage·up to 3.3 volt.
How can I convert·or implement·SX48 port logic high levels down to 3.3 volt?
Thanks for your help!
Murat
Comments
You can use this chip made by texas instruments:
http://focus.ti.com/docs/prod/folders/print/sn74tvc3306.html
See Page 5 in the datasheet for an example for 3,3 <---> 2.5 V (you can change this to 5<->3.3).
I use in one application where i convert 5V to 2.8V I/O.
They work fine for i2c stuff [noparse];)[/noparse]
The send product samples for free if you register.
If you only want to do do i2c writes (for example setting
some registers of another hardware device) and you
do not need to read values you could use
a simple resistor network.
Bye, Simon
Thank you·for the information.
I guess it is good solution! I'll try it.
Bye
Murat
you could also power the SX with just 3.3 Volts (IOW from the same supply that is used for the I²C devices) if your design allows for that. In this case, you don't n need any level-shifters at all. When powering the SX with 3.3 Volts make sure that the brownout detection is either set to 2.2 or 2.4 Volts, or is turned off. You should configure the levels of the input pins connected to SDA and SCL to CMOS in order to set their threshold to Vdd/2.
Besides this, I think that it should also be possible to control 3.3 Volt I²C lines with an SX powered with 5 Volts. According to the I²C specifications, all devices connected to SDA and SCL must be open-collector, and pull-up resistors are used to provide the high-level states. In your case, these resistors should be conncted on one side to the 3.3 Volts supply. The SX port pins driving the SCL and SDA lines must be either configured as inputs (high-Z) to release the lines to their high-levels, or as outputs with low-level in order to pull low these lines.
For reading the status of the SDA, or SCL lines, you should configure the SX inputs for TTL mode. In this case, voltages below 1.4 Volts are considered as low, and those above that value are considered as high, i.e. this threshold comes close enough to the half of 3.3 Volts which is 1.65 Volts.
Greetings,
Günther
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