UART without external crystal

Isaac Puckett

Other Parts Discussed in Thread: MSP430F2274, MSP430F5527

Hello,

I am using the msp430f2274 and I am attempting to transfer strings from my chip to the computer by using PuTTy to monitor the virtual com created by the device. However, the code that I have found in the slac123f.zip file provided for the msp430f2274. Unfortunately, from what I have seen is that all the UART code required a external crystal. Is this mandatory for all communications via usb to the computer or is there a work around?

over 12 years ago

0 Roy Deabill over 12 years ago

Expert 1595 points

Hi,

The external crystal is no mandatory. You can use the DCO to provide the clock to the UART, BUT the internally generated clock options are not as accurate as using an external crystal, so it is possible that you will have problems with getting the bit rate set up accurately.

If you know the frequency of the clock that you are sending to the UART, you will need to adjust the setting in the Baud Rate register to give the appropriate bit rate, and then it should operate OK.

Roy

0 zrno soli over 12 years ago

Guru 34873 points

Roy is right. Also BR divider error have impact on transfer. Here you can find my example with source for MSP430F5527 at 4 Mbps (using DCO, not external crystal)...

http://forum.43oh.com/topic/2972-sbw-msp430f550x-based-programmer/?p=34398

Also, here is my UART setup calculator...

http://forum.43oh.com/topic/2640-uart-configurator

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UART without external crystal