@dc42 , @bearer Here was my mistake:

To configure the magnetometer, I sent

M260 A"0x0C" B"0x60:0x00:0x5C:00" R1

which is nonsense to the firmware.

I stopped using the array of hex values and instead (correctly) used an array of decimal values :

M260 A12 B96:0:92:0 R1

Things started working. Thank you, both.

@dc42 , @bearer I was hoping the clock rate was the issue, here.

M260 A"0x0C" B"0x00" R7

and

M260 A"0x0C" B"0x4E" R7

return the same values:
0x03 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF

The address (0x0C) is correct: it is the default address in the datasheet, and I get errors when I use something else.

B"0x00" is trash, B"0x4E" is a simple read request. Both yield the same "0x03 0xFF....". An explanation is the some configuration is off, and the tail end of the address is being interpreted as the same command. That explanation doesn't make sense, given that the frequency seems to be working as expected.

@bearer Thank you, and I hope both of you forgive my ignorance.

@dc42 According to my o-scope capture of the clock and data lines, the frequency is on the order of 90.91 kHz. So, we know the hardware is operating withing a sane environment.

After looking at baud rate configuration and a few posts about i2c, like this one, I'm still having a communication issue.

I have connected a 3-axis magnetometer with my Duet [FIRMWARE_NAME: RepRapFirmware for Duet 2 WiFi/Ethernet FIRMWARE_VERSION: 2.04RC2 ELECTRONICS: Duet WiFi 1.02 or later FIRMWARE_DATE: 2019-08-05b1]. I have connected them through TWD0 and TWCK0 pins, using i2c. The baud rate for the magnetometer is 9600. The buad rate for the Duet is 57600.

I don't seem able to change the baud rate with the M575. Using M575 P1, I could change the baud on PanelDue , but it doesn't seem to support i2c.

Is there an i2c port on the Duet that permits a change in baud rate?

Thank you for your time, in advance. sjm