UART with I2C bus interface

I'm looking for a UART component with I2C bus interface as a stand-alone part. So far I have only been able to find 16550 type devices in large multi-pin packages. Is there such a thing? I would like to have option of 3.3 or 5.0V VCC powering.


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I have never seen an UART with I2C interface ( to the host I suppose )

maxim does an UART with SPI interface

or you can use a microcontroller with slave I2C peripheral and UART to do the translation, some high speed micro could do all in software

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The application of such a device intrigues me, a PIC16F88 + a bit of code would do the trick. EEPROM in the PIC would allow the programming of different slave addresses. Or you could config the slave address with port lines. 5V or 3.3V is no problem - use a PIC16LFxx for 3V

-Andrew M

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Andrew M

"wb0gaz" schrieb im Newsbeitrag news:

I don't know of any universal part which does this.

  • Do you need the I2C to be slave or master?
  • What maximum speed do you need?

Acting as I2C master should be fairly easy, slave mode is much more complicated because you need to wait for data in slave-receiver mode and not all masters support clock stretching.

The key problem is that RS232 supports independent transmissions in either direction while I2C is a master/slave bus.

If I were you I'ld go for a hand-made uController solution. There are solutions for level shifting, see

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Roland Zitzke

Hello Roland,

Thanks for the posting. As usual, I've not adequately specified the problem!

Basically I envision the proposed I2C-UART device to be a slave (the microcontroller in the system would be the master); routine async baud rates such as 9600, 19200, 38400 bps, etc., would be the typical data rate involved.

As I found nothing in this search, I believe making a small microcontroller be the UART would be the likely solution. I guess $3 microcontroller has obsoleted a $3 UART! It's all part of the learning curve, I'm learning.....

Thanks again,


Roland Zitzke wrote:

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Please understand that there are sticky timing issues with an I2C slave. At a minimum, the I2C hardware must be able to stretch the transfer cycle with clock clamping.

The main cause for the timing problem is the fact that the master controls the transfer. The clock clamping is the only means of a slave to get some reaction time. Of course, the master has to be able to honour the clock clamping.

When selecting the microcontroller make sure that the internal I2C hardware is able to run as a slave and handle the clock cleamping in the hardware - there's simply not enough time to do it in software alone.

Tauno Voipio
tauno voipio (at) iki fi
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Tauno Voipio


have a look at the Philips LPC915 (or for that matter 916 / 917). The only thing it needs is power and ground. The internal oscillator is good enough for the UART, across the whole temperature range, the I2C is synchronous anyhow and 2k Flash combined with 128 bytes RAM is plenty for what you are looking for.

Info would be here:

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The appropriate evaluation board could be the MCB900 from Keil which comes with a 4k compiler.

H> I'm looking for a UART component with I2C bus interface as a

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An Schwob in the USA

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