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arduinosensorsi2cpic32

I2C communication between pic32 and MPL3115A2 Altitude/Pressure Sensor

I'm trying to do something really simple and I'm having a bit of trouble getting it to work. I'm working with the MPL3115A2 Altitude/Pressure Sensor and a pic32 uC32 board, and I'm trying to communicate between the two using I2C. (uC32 board is similar enough to arduino that it's practically the same in terms of coding).

I'm using the wire library and I'm simply trying to read register 0x0C from the MPL3115A2, which should give me the device ID.

Here's a code snippet (the define is at the top of the code and the rest is in the main loop):

#define barAddress 0x60

Wire.beginTransmission(barAddress);
Wire.send(0x0C);
Wire.endTransmission();

Wire.requestFrom(barAddress, 1);
uint8_t a = Wire.receive();
Serial.println(a, HEX);

So I start the transmission with address 0x60 (From the datasheet: The standard 7-bit I2C slave address is 0x60 or 1100000. 8-bit read is 0xC1, 8-bit write is 0xC0.). Then I send 0x0C because that's the register I want to access. I then end transmission, and request 1 byte from address 0x60, receive that bit into a 8-bit variable, then print it.

The problem I run into is that when I print it, I just get 0. I don't get the device ID, just 0. No matter what register I try to read, I get 0.

I've been banging my head against a wall for the past few days trying to get this to work. I've attached something I've captured with a logic analyzer, as well as a list of registers from the datasheet of the MPL3115A2 that I've been trying to access.

Using a logic analyzer I can see the clock and data lines. The clock seems normal and the data line gives me the following:

START
Write['192'] + ACK
'12' + ACK
STOP
START
Read['193'] + ACK
'0' + NAK
STOP

This all seems correct to me (192 and 193 come from 8-bit write and read being 0xC0 and 0xC1), except for the '0'. I should be getting the device ID, not 0.

Thanks for any help with this!

Solution

  • You should look at Freescale's app note AN4481, which is referred to by the datasheet. Page 5 shows the single-byte read operation which is what you are doing, except that the register address write must not be followed by a STOP but instead uses a REPEATED-START.

    I'm not familiar with the Wire library but it look like all you need to do is remove the Wire.endTransmission(); between the send and requestFrom.

    Hopefully, this will solve your problem.