TPIC84000-Q1: SPI configuration

Hi Gerardo,

Sorry we missed your question. Were you able to find an answer? If not, let me know and we'll help you out.

Best,

Grant

Hi Grant,

I already communicated with the TPIC. However, it always reply me with 40 00 00 00 in the last bytes of both registers. Why can be that possible? I checked that the command is sent properly with an oscilloscope, and I always receive such last bytes.

Also, how can I be sure that the device is waken up, apart from the register? Because I cannot be sure with the mistake I described before.

And I did not find an answer neither to the last question. Which is the correct configuration?

Thank you,

Gerardo

Hi Gerardo,

Thank you for your patience. Let me contact the team that supports this line of products. They should be able to answer your question within the next few days.

Best,
Grant

Gerado,

Sorry for the delay. I will assist you with your questions.

For #1, the device should mimic back what you wrote on the previous command. If it is sending 0x40 00 00 00, then it thinks you wrote all 0's to data register 2. Can you send the hex commands in sequence that you are sending to the TPIC? I can look through it to try to figure out what is going on. As for the intuitive communication interface, I think there is a GUI and communication card that will make communicating with the device easier. I will check to see if it might be something we could get to you.

For #2, to determine if the device has woken up, you should be able to monitor the device current draw from AVDD and DVDD (the 5V supplies). If the device is awake, the total current draw on these pins should be ~20mA.

For #3, each OUTx should be connected to a separate antenna. The other end of the antenna should be connected to ground. This way you can get all 8 channels working for 8 separate antennas.


Let me know if this helps and if you have any more questions. Thanks.

Regards,
Darren

Darren,

Thank you so much for your reply.

For #1, please find attach a file with the commands I am trying to use and what I think it is expected to receive from the TPIC.

In addition, I have some doubts about TPIC related to my design:

1 - I want to use a loop as an antenna. Would it be possible? How can I connect it? Should it be one side to an output, and the other to ground?

2 - In order to tune the loop to 134,2KHz, where should I put the capacitor and resistance? Between the output of the TPIC and the loop?

3 - Which current is usual through an output?

4 - How can I measure in an oscilloscope the output of the TPIC? Where should I connect it to see the 134,2KHz signal?

5 - How does the environment influence to transmission? I want to use the loop over several materials, how can this fact affect?

Thank you so much in advance,

GerardoTPIC Commands.xls

Gerarado,TPIC84000 sample code.xlsx 

Thank you for the command file. I think one issue is when you send the device all 0's (your second command). I do not think this is a valid command. If you want to read back the previous command, I think you need to send 0x80 00 00 00 00 00 00 00. I have attached a snippet of sample code that I have used before to send data out on OUT1.

I apologize if the spec is a little confusing - it looks like all 0's should be valid according to the spec, but I think it really isn't. This device was actually originally a custom device designed for a specific customer (who controlled the datasheet), and we negotiated open market rights for it, so we had to convert their datasheet to one of ours. If we had built this device as a catalog part from the beginning, we would have a much better datasheet. That being said, I will try everything I can to resolve your issues so you will have a successful project.

 

Now to answer your questions:

1 - I think a loop antenna should be fine. Do you have any specs (inductance, resistance, saturation, etc.) so I can look at it to make sure? You should connect one side to OUT1 (or whatever output you want to use) and the other to ground.

 

2 - To tune the output, it should be device output-->resistor-->cap-->antenna. These should all be connected in series. The resistor is a dampening resistor and might not be 100% needed, but it is a good idea.

 

3 - The usual current through the loop/output is 25mA max. The actual current will depend on the impedance of your antenna and the gain set for the output.

 

4 - You can connect the scope directly to the OUT1 pin on the device to see the output waveform. You can disconnect the antenna when you monitor the waveform to eliminate the loading so the voltage levels will be what you set in the gain (assuming there is enough VS voltage. you need a VS voltage of something like the output voltage +2V)

 

5 - The environment can affect the transmission distance of the antenna, as well as the frequency of the signal. If you start in air, but then transmit through some other material with a different 'n' value than air, it will change the frequency of the transmission. It has been a while since I have reviewed this, but I think as long as the receiver and transmitter are both in air (or the same material) the transmitted and received frequencies should be the same. The shift that happens when the EM wave goes from air to another material is undone when it comes out of the other material and back into air (I think). But if you are transmitting from air into something else, like water, you need to account for the shift on the receiver.

Hi Darren,

Thank you so much for your reply.

About the sample code you attached, I already found it in the forum. The point is that it did not seem to work for me, with the same problem I quoted before. Could it be some problem in the TPIC registers? Can they have some failures with some kind of over current?

Is there available another sample code? Apart from the all 0's command, is there anything else wrong in my code?

Thank you so much in advance,
Gerardo

Gerardo,

If the code isn't working, we should take a step back and make sure everything is configured correctly. I have module with the TPIC84000 on it, but we recently moved lab locations, and it is somewhere in storage. Once I find it, I can get you actual plots and exact measurements, and newly tested code, but for now we will rely on my memory of when I last tested the device and old test documents. I did not see anything else wrong with your code.

Earlier I had said the current limit for the device was 25mA. This is incorrect. It is 25mA/LSB when doing the current read back, depending on the selected range. The actual current limit for each channel is minimum of 1.2A. If there is an over-current event, I don't think the TPIC shuts off the transmission, it just limits the current to the max, and sends the over-current flag. So I do not think it is an over-current causing the issue here.

There are a few things we can try to debug this issue.

1 - When you first connect DVDD and AVDD how much current do you see? Can you try to send only the wake-up command 0x90 00 00 00 00 00 00 00? The current should jump from <2mA to ~20mA. Do you see this? If so, it means the device is configured correctly and the SPI fram is correct. If you send 0x90 00 00 00 00 00 00 01, it should go back to sleep (<2mA current). If you do not see the device respond to these commands, can you provide a scope plot of the SCLK and SD pins?

2 - I just remembered that you need to supply an external clock to the device. Are you doing this? It should be a square wave of 0V-5V and 2MHz.

3 - can you measure the current coming out of RBIAS? There needs to be a 62kOhm resistor to ground on this pin. This sets the internal current reference. I think the device will actually work if it isn't 62kOhm, but the current measurements and output voltage levels wont be correct.

Once I find the TPIC84000 module I will provide you with my exact commands and scope plots so you can compare them to what you see.

Regards,

Darren