The I2C interface does not have any pull-up resistors on the board, these should be provided elsewhere, most probably with the bus master.

They are required on both the SCL and SDA lines, but only once for the whole bus, not on each module. I suggest a value of 1k8 if you are

going to be working up to 400KHz and 1k2 or even 1k if you are going up to 1MHz. The compass is designed to work at up to the standard

clock speed (SCL) of 100KHz, however the clock speed can be raised to 1MHZ providing the following precaution is taken;

At speeds above around 160KHz the CPU cannot respond fast enough to read the I2C data. Therefore a small delay of 50uS should be

inserted either side of writing the register address. No delays are required anywhere else in the sequence. By doing this, I have tested the

compass module up to 1.3MHz SCL clock speed.

Pin 7 is an input pin selecting either 50Hz (low) or 60Hz (high) operation. I added this option after noticing a jitter of around 1.5° in the

output. The cause was the 50Hz mains field in my workshop. By converting in synchronism with the mains frequency this was reduced to

around 0.2° . An internal conversion is done every 40mS (50Hz) or every 33.3mS (60Hz). The pin has an on-board pull-up can be left

unconnected for 60Hz operation. There is no synchronism between the PWM or I2C outputs and the conversion. They both retrieve the most

recent internal reading, which is continuously converted, whether it is used or not.

Pin 6 is used to calibrate the compass. The calibrate input (pin 6) has an on-board pull-up resistor and can be left unconnected after

calibration.

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Pins 5 and 8 are No Connect. Actually pin 8 is the processor reset line and has an on-board pull-up resistor. It is there so that we can program

the processor chip after placement on the PCB..