3 to 8 Decoder with both I2C and TTL control

[Sariel]

Hello,

I am looking for an IC that allows to decode (I/O expender) 3 to 8 bits.
There are several devices as this with I2C interface such as PCF8575.
But I am looking for a device, that has I2C interface and also an option to configure the 8 output bits manually usuing TTL or pullup/pull down resistors on 3 input bits.

Are there any such devices ICs?

[Ian.M]

Why would there be?  The assumption ever since Philips came up with I²C is that there is a MCU or CPU 'in the loop' to handle configuration, so if it *is* possible to configure an I²C  device to power up standalone in a particular selectable state, that configuration will be done over I²C .

If you *need* that functionality, you are probably going to have to roll your own I²C slave on a MCU or FPGA with enough I/O pins to let you have 'override' inputs.

[mikerj]

Hello,

I am looking for an IC that allows to decode (I/O expender) 3 to 8 bits.
There are several devices as this with I2C interface such as PCF8575.
But I am looking for a device, that has I2C interface and also an option to configure the 8 output bits manually usuing TTL or pullup/pull down resistors on 3 input bits.

Are there any such devices ICs?

A 3 to 8 line decoder (e.g. 74LS138) will not allow you to configure 8 output pins separately, a 3 bit code only permits selecting one of 8 possible pins at a time.  This would be an extremely unusual requirement, I don't think you'll find anything off the shelf.  You could create this function with a bus expander, a separate 3-8 decoder and some selection logic to tri-state the decoder when not used.

[dobsonr741]

Time to roll a small MCU. Code an I2C slave, add the combinatorial logic. I’m doing about the same, as I run out Holtek LED drivers, and a small MCU to replace it.