Note that U4, a 10 MHz MEMS oscillator, is also very close to the microcontroller’s clock input pin. It’s always a good idea to minimize the length of traces carrying high-frequency digital signals. First of all, there are noise benefits: a shorter, more direct trace reduces the amount of noise that would otherwise be coupled into adjacent traces, and a shorter trace also reduces electromagnetic interference (EMI) because it is less effective as an antenna. The second issue is related to transmission-line effects. Minimizing trace length is a simple way to avoid problems related to signal reflections. However, reflection is not a significant concern at frequencies in the 10 MHz range, unless you are dealing with long interconnections or a very large PCB.
Although this device uses an I2C interface with communication speeds up to 1 MHz, two of the eight pins are dedicated to Alert (pin3) and nReset (pin 6). The Alert pin is intended to be connected, if desired, to an interrupt pin on a microcontroller. According to section 3.5 (ALERT Pin) of the datasheet, "The output of the pin depends on the value of the temperature reading relative to programmable limits," and its function is "explained in a separate application note.
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