I'm programming my LPC1313 MCU with Flashmagic on my mac and I am asked to put in the baudrate along with the Xtal frequency. I'm not sure what those are and when I looked in the data sheet I found no information about it. What do those terms mean in terms of a microcontroller and how can I determine the Xtal frequency and the baudrate of the LPC1313 MCU?

  • \$\begingroup\$ Crystal details will be in the board documentation. \$\endgroup\$ – Leon Heller Jun 11 '13 at 15:56
  • \$\begingroup\$ @LeonHeller I couldn't find the values for the baud rate or the Xtal Frequency \$\endgroup\$ – Coder404 Jun 11 '13 at 15:57
  • \$\begingroup\$ Xtal = Crystal in short hand \$\endgroup\$ – Spoon Jun 11 '13 at 18:01
  • \$\begingroup\$ Presumably, the programming itself is not being done over a serial port, but rather over USB. A possible reason for entering the crystal frequency and baud rate might be that this Flashmagic configures the serial port on the device to a particular default baud rate that comes into effect when the device is powered up so that, e.g. the firmware can communicate with a serial console. Baud rates are often set by programming special registers with values the specify the baud rate as a clock divisor. The values are dependent on clock rate. \$\endgroup\$ – Kaz Jun 11 '13 at 18:48
  • \$\begingroup\$ Crystal could also refer to the oscillator which drives the system clock \$\endgroup\$ – Spoon Jun 11 '13 at 20:06

Did you try Wikipedia?

In telecommunication and electronics, baud (/ˈbɔːd/, unit symbol "Bd") is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes (signaling events) made to the transmission medium per second in a digitally modulated signal or a line code. The baud rate is related to but should not be confused with gross bit rate expressed in bit/s.

Ostensibly, there is some serial protocol you are configuring, and you have to say how fast it should go.

"Xtal" means "crystal". The clock for your MCU is probably controlled by a crystal oscillator. The MCU can only interpret units of time relative to this clock, and you have to tell it how fast the crystal you are using is, probably so it can convert the baud rate you've configured in "symbols/second" into "symbols/clock pulses".


protected by clabacchio Jun 11 '13 at 17:58

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