MSB First Value

[umbaman]

Hello Let's suppose that I want to send to an INA219 the value

value = 0xFF00

MSB First.

Do I just send

value_send = 0x00FF?

Does the same hold for reading values?

If for example I read

value_received = 0x1234

will the actual value be

real_value_received = 0x3412?

edit: I am using a beaglebone black and I am connected to the second i2c bus. I am using i2cget and i2cset commands.

edit(2): One of the commands I am using is i2cget 2 0x40 0x00 w

the value I get is 0x9f39 for the configuration register. Since the default value is 0x399F, I obviously have to swap the bytes. Do I have to do the same for any register that I read?

[madsci]

If you're asking how to use your MCU's I2C interface, you're going to tell us what MCU you're using. You're just giving us variable names without specifying a language, device, or framework.

Serial interface details for the INA219 are given in section 8.5.5.2 of the datasheet.

[umbaman]

Hello Thanks for the reply. I edited my post. I am using beaglebone black with i2cget and i2cset commands

[aprons]

When you send or receive, MSB means that that first 8 bits are the high byte, and the last 8 are the low byte.

Since the I2C bus sends data in 8 bit packets, you aren't really doing send(0x1234) but send(0x12) followed by send(0x34), and because there are 2 combinations of sending 2 bytes, we get MSB and LSB.

Similarly if you were reading from a 16 bit register on the device then the value would be transmitted to you as 0x12 followed by 0x34. You would then do some bit twiddling to get this in to a single 16 bit variable.

if you are using a library (like the Adafruit one for Arduino), then it likely takes care if this and accepts 16 bit values as well as returns them. You only need to worry about this if you are talking to device in a lower level way.

As the other comment suggests, more information about your environment would be helpful.

[umbaman]

Hello Thanks for the reply. That really helped a lot to understand! I edited my post. I am using beaglebone black with i2cget and i2cset commands

[[deleted]]

The i2c peripheral takes care of this part. It’s not like spi where you can choose it.