I2C SDA Low

[Makaram]

Hi guys, I've been trying to get TCM8240 camera working and I cant seem to get I2C right.
My problem seems to be that SDA is always low, and yes I've tied it high.
SCL is high as required yet, SDA remains low.
This is right from the get go, even if the camera module is held on reset.
Also there is not continuity to ground

Any help would be appreciated

Thanks

Matt

 

[Ian Rogers]

First you need to isolate the problem... Have you got a different I2C device at least to try? If the camera is holding the SDA line low then there's more than likely a fault with the camera.

You have been struggling with this for quite a bit now...

 

[Makaram]

Been full on with work (Out of town) Finally got some down time.
I thought my problem was my I2C driver for ages because I was getting ACK bits. But really that was just checking to see if the slave pulled SDA low, which it always is.

Just to confirm.. This isn't normal behavior ? I can drive it high and judging by the voltage drop across my 1k resistor, I think the resistor pulling it low is 240 Ohmish.

Do some products do this to indicate an issue with power supply or clock pulse??

 

[Ian Rogers]

I think the resistor pulling it low is 240 Ohmish.

Is this the assumed pulldown inside the slave?

 

[Makaram]

That or some flaw. SDA is around 500mV and I have a 1kOhm pullup to 2.8V

 

[Ian Rogers]

2.8V ?? can the camera operate that low??

 

[Makaram]

That's the norm

 

[Ian Rogers]

Yes, I see ( I just read the datasheet)...

You'll have to get a small I2C ram and try to see if it works with that.

 

[Jon Wilder]

I've never worked with PIC32 but on the PIC's that I have worked with, the SDA and SCL pins must be tristated in order for the MSSP module to have control of the pins (TRIS bits = 1 for those pins on 16F and 18F). This allows the MSSP module to operate them in open drain fashion. Has this been addressed?

 

[Makaram]

Yeah unfortunately thats not the issue. I think its an issue with either the camera itself or my soldering :S

 

[Ian Rogers]

In the datasheet it talks about power down mode and standby mode where ALL output pins are kept low.... It doesn't, however, state if the IIC pins are treated the same...

I can't see that being the issue but there is a definite switch on sequence to get the device out of powerdown mode..

 

[Makaram]

Oh god