Adding note about I2C 400kHz issues.

Author: nseidle

README.md

@@ -1,4 +1,4 @@
-SparkFun Ublox Arduino Library
+SparkFun u-blox Arduino Library
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@@ -18,10 +18,18 @@ SparkFun Ublox Arduino Library
  </tr>
 </table>
 
-Ublox makes some incredible GPS receivers covering everything from low-cost, highly configurable modules such as the SAM-M8Q all the way up to the surveyor grade ZED-F9P with precision of the diameter of a dime. This library focuses on configuration and control of Ublox devices over I2C (called DDC by Ublox) and Serial. The UBX protocol is supported over both I2C and serial, and is a much easier and lighterweight interface to a GPS module. Stop parsing NMEA data! And simply ask for the datums you need.
+U-blox makes some incredible GPS receivers covering everything from low-cost, highly configurable modules such as the SAM-M8Q all the way up to the surveyor grade ZED-F9P with precision of the diameter of a dime. This library focuses on configuration and control of u-blox devices over I2C (called DDC by u-blox) and Serial. The UBX protocol is supported over both I2C and serial, and is a much easier and lighterweight interface to a GPS module. Stop parsing NMEA data! And simply ask for the datums you need.
 
 This library can be installed via the Arduino Library manager. Search for **SparkFun Ublox**.
 
+
+Max (400kHz) I2C Support
+-------------------
+
+To achieve 400kHz I2C speed please be sure to remove all pull-ups on the I2C bus. Most, if not all, u-blox modules include pull ups on the I2C lines (sometimes called DDC in their manuals). Cut all I2C pull up jumpers and/or remove them from peripheral boards. Otherwise, various data glitches can occur. See issues [38](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/issues/38) and [40](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/issues/40) for more information. If possible, run the I2C bus at 100kHz.
+
+-------------------
+
 Want to help? Please do! We are always looking for ways to improve and build out features of this library.
 
 * We are always interested in adding SPI support with a checkUbloxSPI() function
@@ -38,8 +46,7 @@ Thanks to:
 * [grexjmo](https://github.com/grexjmo) for pushing for a better NMEA sentence configuration method
 * [averywallis](https://github.com/averywallis) for adding good comments to the various constants.
 
-
-Need a library for the Ublox and Particle? Checkout the [Particle library](https://github.com/aseelye/SparkFun_Ublox_Particle_Library) fork.
+Need a library for the Ublox and Particle? Checkout the [Particle library](https://github.com/aseelye/SparkFun_u-blox_Particle_Library) fork.
 
 Repository Contents
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