Adding TWI communication with accelerometer to BLE

RE: Adding TWI communication with accelerometer to BLE

bneil — Tue, 15 Mar 2016 23:25:03 GMT

I was just playing around with this stuff as well. If you look at the datasheet for the accelerometer they're using in the example, the address is actually 0x4c. When shift that up you get 0x98. What I believe is happening (I'm still learning this stuff myself) is that they are writing the address like that because there needs to be room for the read/write bit to be set, but to be honest, that's a guess.

RE: Adding TWI communication with accelerometer to BLE

Fabien Comte — Tue, 01 Mar 2016 19:45:09 GMT

Do you have some 4.7 Kohms external pullup resistors ?

RE: Adding TWI communication with accelerometer to BLE

MR2 — Fri, 26 Feb 2016 11:30:16 GMT

I think I corrected my problem but I am unsure whether the correction is right or not: In the twi_sensor example, the address of the sensor is defined like this:

#define MMA7660_ADDR        (0x98U >> 1)

the ">> 1" probably refers to the following description of the twi functions: [in] address Address of a specific slave device (only 7 LSB). However, when I use the same syntax for the MMA8452Q device, i.e.:

#define MMA8452Q_ADDR      (0x1DU >> 1)

the device never answers to any read or write requests. When I remove the ">> 1" everything works perfectly. Is this correct to remove the ">> 1" in my case? And why?