18M2 RTC

[Tony P]

I am trying to connect an RTC to the CH1030A project board but cannot get it to work. I am using the centre non-buffered pins B.1 (SDA) and B.4 (SCL) as normal but I am not getting the RTC to run.
I have tested the 18M2 and the RTC on the AXE091 project board and all work fine.

Any ideas please?

 

[The bear]

The clever people on this forum will ask you for more information.
Like: Photo of layout, circuit diagram, your coding & symptoms (What it is or isn't it doing). I'm not clever.
Good luck.

 

[Hemi345]

Do you have the 4.7K pullup resistors fitted? The AXE091 has those built in (to the right of the RTC).

 

[hippy]

Also check your power rail. If the power rail drop below some level ( 4.5V ? ) in comparison to the battery back-up voltage the RTC can think it's unpowered, will disable its I2C interface.

But my gut feeling is Hemi345 has nailed it with missing pull-ups.

 

[Tony P]

Do you have the 4.7K pullup resistors fitted? The AXE091 has those built in (to the right of the RTC).

No I dont. I didn't realise that I needed them!.
But I have other clock circuits happily running, such as a central heating time clock, using 18M2 and the same RTC's without the resistors!

 

[hippy]

But I have other clock circuits happily running, such as a central heating time clock, using 18M2 and the same RTC's without the resistors!

Some RTC modules may have the pull-up resistors included on them.

It may be possible to get I2C working using the internal pull-ups so would be worth adding "PULLUP %00010010" to the start of your program. If that makes the RTC work, stops when you take that out, then it's almost certainly a pull-up issue.

Also double-check you haven't got SDA and SCL crossed over.

 

[Tony P]

Sorted thank you.
The RTC module that I used for my heating time clock has indeed got the required pull ups. This new RTC has not even though I purchased them as a job lot of, what I assumed were, identical modules.
Two 4k7's added and I'm all good to go