Can anyone identify the protocol for this transmitter?

I am trying to figure out the communication protocol of the transmitter chip found inside an RC remote (FS-GT2B). Originally, I thought it was I2C but after some research it seems less likely because it is lacking some characteristic lines. The silkscreen says "SCK", "SCS" and "SDIO". Here's a picture of the chip: If someone can identify this, it would be very much appreciated.

Thanks.

Sounds like Clock, Chip Select, Data In -> SPI?

Hi I tried to use a Saleae Logic to decode the SPI but I am not sure what the bit/transfer is. By default it is set to 8 in the logic analyzing software but decoded values change when I change it to 10 bits. How do I know for sure which one it is?

This is what I got with the following settings on SPI mode.

If sizing of picture is an issue use: http://i.imgur.com/8bCanXO.png

Thanks.

If its Atmel AVR hardware-based, its 8 bits. Not changeable. If its bitbanged (software created), then who knows.

Hmm maybe I can look around on the PCB more for an Atmega or something. Do I have to look inside the chip? Also, does the existence of atmel hardware guarantee it's bitbanged?

There’s no guarantees. I’ve seen people doing software bitbanging on the hardware pins! What a waste.

Looks like SPI as Crossroads says. It also looks like 8 bit data and it's sending 2x 8 bit per CS toggle apart from the 4 bit clock to start with but that could be poorly selected trigger. You may need to mess with the bit order and CPOL/CPHA to get meaningful results though.

Thanks for the reply. Can you detail what a normal SPI output for something of this sort should look like?

lpbug: Thanks for the reply. Can you detail what a normal SPI output for something of this sort should look like?

The image you supplied looks like SPI but your channel 0 values you show in your logic analyzer capture will change value depending on bit order and if data is clocked in on leading/trailing edge of clock signal. Maybe some radio control forums will break down the RF protocol used by the FS-GT2B (or any transmitter) so you can compare what you think your capturing to what you should be capturing.

sorry for the hijack, but what oscilloscope are you using here please?

Thanks Riva, I will do that.

Kelvin, I was using the Saleae Logic

lpbug: Kelvin, I was using the Saleae Logic

$149! thats a freaking bargain! would you rate it?

it's very nice. I am using the one from my lab. I actually was looking around on eBay and there is a clone that sells for $14. I am going to try that one out as I have to return the one I currently have to the lab that I'm working at.

kelvinmead:

lpbug: Kelvin, I was using the Saleae Logic

$149! thats a freaking bargain! would you rate it?

I find a logic analyser to be a much more helpful tool for microcontrollers than an oscilloscope. I have one of these that is perfectly suitable for most stuff I do but I also bought one of these and it also does the job okay.