Interfacing MMA7455 SPI to CY8Kit-042

[Anonymous]

 Hello,

       

I'm at my wit's end with this, but I absolutely cannot for the life of me get this accelerometer to work with this board in any way shape or form. I first tried I2C, but this plain does not work despite the fact that the sensor claims to support I2C. I keep getting NACK's back when sending a start with the correct slave address. 

   

So I'm trying SPI. This *appears* to work. I'll send the master control data to the master control register, however when I attempt to read back the status register from the rx buffer, the rx buffer simply contains the very last data I sent from the tx buffer. To be clear, the break out board does not support 4-wire SPI, only 3-wire (bidirectional) which is how I have it set up. 

   

The sensor's data sheet is: http://parallax.com/sites/default/files/downloads/28526-Freescale-MMA7455L-Device-Documentation.pdf

   

Of particular interest are pages 9 and 18. 

   

I've done everything I can possibly do over the course of 2 weeks to get these two devices to play nicely and they just don't seem to want to whatsoever. I've attached the workspace.

[Bob_Marlowe]

Welcome in the forum and in the fascinating and sometimes complicated world of PSoCs!

   

I have several accellerometers and magnetic compasses connected to a PSoC 4 and 5 with I2C, and it did work pretty good. When you still have the project that interfaces to I2C I will have a look at when you upload it here. To do so, use
Creator->File->Create Workspace Bundle (minimal)
and attach the resulting file.



Bob
 

[ETRO_SSN583]

One common problem with integrated and conditioned sensors is power

   

up delay, as well as command delay. Check datasheet for those gotchas.

   

Usually in the "fine" print notes.

       

There is a contact at the bottom of this thread you might use if forum

   

cannot solve issue. www.element14.com/community/community/designcenter/psoc4_pioneer_kit/blog/2013/12/01/smarter-

   

life-challenge-smart-bicycle-light-update-5

       

Regards, Dana.

[Anonymous]

 Thank you Bob for the help.

   

Here is the minimal workspace for the I2C project. I've commented a few lines indicating what is returned from I2CMasterSendStart.

[Anonymous]

 I forgot to mention that for my I2C circuit, I am using external 4.7k pull up resistors to the 5VDC source.

[Bob_Marlowe]

Stay tuned, here is dinner-time, will take 2hrs...

   

Bob

[Bob_Marlowe]

Ha! Short glimpse reveils your first error: slave address is 0x1d. So why do you shift it left?? leave it as it is, the component handles all of that. Place a #define for the slave address, so there are fewer changes needed.

   

Bob (now going into the kitchen)

[Anonymous]

 Thanks for your time,

   

I did try the 0x1D as well for the slave address and get the same results. First status is 0x02. After another attempt it is 0x04.

[Bob_Marlowe]

So, some more questions: What board are you using? An own?? a Pioneer kit???

   

Probably a Pioneer since you are using P4_0 and 1 for I2C. These two pins already have got pullup resistors and are dedicated for I2C. Remove the additional pullups or use alternate pins P3_0 and 1

       

You tell that the error is "Last byte NAKed", but that's not a valid status for SendStart() afaik, please check the result again.

   

When an error occurs at SendStart() you may wait a bit of time (as you did) but you have to stop and re-start the I2C-component

   

You specified 1000kb transfer-rate, datasheet tells no "HS" better use 50 and increase later, when working.

   

After SendStart you should go on, or the bus will "hang"

   

Write a byte WhoamI register (0x0F) with WriteByte()

   

then a SendRestart() to read

   

and then read from device with ReadByte() NAKed (should read 0x00)

   

and finally a SendStop ()

       

Happy coding

   

Bob

[Anonymous]

 Thanks Bob,

   

I didn't know about the internal pull up resistors. I will remove them and try everything you said. Concerning the NAK error, on pg. 27 of the SCB documentation it indicates that SCB_I2C_MSTR_ERR_LB_NAK is an error, which is the first one returned.

[ETRO_SSN583]

The pullups on Pioneer 2.2K, your 4.7K will not really effect anything as the

   

1.5K result, PSOC 4 has enough drive to handle both.

       

Regards, Dana.

[Anonymous]

 Thanks for the suggestions.

   

None of them, however, are working. I tried to stop the I2C component, restart it, send a start again, followed by attempting to read from the Whoami reg, and the program hangs on WriteByte(0x0F). The SendStart calls are still returning 0x02 (NAK).

       

I removed the external pull up resistors as well as dropped the transfer rate to 50kbps.

       

I've never had this much trouble interfacing a sensor. I'm throwing my hands up here, this is totally baffling.