Discussion in "General help Guidance and Discussion" started by    er    Dec 12, 2013.
Thu Dec 12 2013, 10:26 pm
#1
Hello everyone,

I am trying code MMA7455 Accelerometer in SPI mode. I am not able to retrieve any data from it. I have issue with addressing register of MMA7455.
After googling what i found is actual register addressing is done by..

function_to_write((addr)&0x3f)<<1);


can anyone help me to explain it..
Sat Dec 14 2013, 03:20 am
#2
If your don't have a very good understanding of SPI you will be
lucky to get the MMA7455 to work !
It can be either I2C or SPI and has 3 or 4 wire SPI.
Use other peoples designs and code where possible.
To answer your question..
The data sheet says
"The write command consists of an MSB (0=read, 1=write) to indicate
writing to the MMA7455L register, followed by a 6-bit address
and 1 don’t care bit."

Your code isolates the 6 bit address using &0x3f
It shifts the 6 bits one place to the left using <<1
Then sends the result.
In this case the top bit will be 0 meaning a read request.
The bottom bit will be zero.. but is the "don’t care bit."


[ Edited Sat Dec 14 2013, 03:21 am ]
Sat Dec 14 2013, 05:25 pm
#3
i am done with interfacing.. and it works..

But MMA7455 supports 2g,4g and 8g mode sensitivity. Can you tell me how this will affect raw data of acceleration???

datasheet says 2g = 64LSB/g. How to interpret it?? What does it mean..????
Mon Dec 16 2013, 02:58 am
#4
MMA7455 is a digital sensor so output is in digital format unlike some analog sensor which gives output as V/g and in this digital sensor its LSB/g or mg/LSB

you can convert 64LSB/g to mg/LSB as 64 mg/LSB which means.. if your digital output is
0000 0000 = 0g
0000 0001 = 0.064g
0000 0010 = 0.128g
... and so on...

Hope you get it now?

Get Social

Information

Powered by e107 Forum System

Downloads

Comments

Bobbyerilar
Thu Mar 28 2024, 08:08 am
pb58
Thu Mar 28 2024, 05:54 am
Clarazkafup
Thu Mar 28 2024, 02:24 am
Walterkic
Thu Mar 28 2024, 01:19 am
Davidusawn
Wed Mar 27 2024, 08:30 pm
Richardsop
Tue Mar 26 2024, 10:33 pm
Stevencog
Tue Mar 26 2024, 04:26 pm
Bernardwarge
Tue Mar 26 2024, 11:15 am