Thread: Software I2C - Not getting ACK from slave

Hi

I have started to implement a software i2c driver.

I have run the function on several devices on a custom PCB.
Below is the logic output directly from the bus.

Of the 4 devices tested so far, only one of them has returned an ACK. The others are not replying.
All of these slave devices are wired correctly and there is no reason why they should have failed. So at this point im focused on the software as the issue.

You can see that the analyser is correctly picking up whats been sent. 0x55 is the base address with a write bit. The device in particular is a BQ27441.

From the logic output shown, is there anything glaringly obvious as to why im not getting responses from most of the i2c devices?
Each device is on its own bus, so theres noting else that can interfere. not required i know, but i had a load of pins spare and it made routing much better.


PCB

The trace looks good, and the address matches that in the datasheet so I guess it is something physical.

I did something similar to this a while ago, on TI 16-bit DAC. Got as far as reflowing a new part on. 0.5mm pitch, really panful.

Problem was that I was using the wrong device address - opps!

Originally Posted by stahta01

The docs I read had

Code:

#define GAUGE_DEVICE_ADDRESS 0xAA

Is there a reason you are using the address shifted one bit over?

Or is the graphic wrong about address 55?

Tim S.

High 7 bits are the device address, lowest bit indicates if it is a read or write transaction. So commands to device 0x55 will begin with either 0xAA or 0xAB.