MSP430F5xx USB - UART max frequency 1 MBAUD?

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on Apr 17 2012 14:43 PM

Expert2800 points

All:

The UART spec is 1 MBAUD. I have an application where the ideal BAUD rate is 1.024 MBAUD - how flexible is the spec in this regard?

If we cannot get to t 1.024 MBAUD, then, we would have to back off to 512 KBAUD.

All of this is because of the processor being connected to the MSP430, and the inflexibility of the clocking that it can use.

Regards,

Todd Anderson

All Replies

Posted by TonyKao

on Apr 17 2012 15:43 PM

Genius3770 points

Hi Todd,

If you're sourcing the UART with an accurate clock source (eg crystal and preferably one that divides nicely into 1.024MHz) then I don't see why you cannot do 1.024Mbaud.

However, you should test the transmit-receive error rates at both 1.024MBaud and 512KBaud and see if they are acceptable, and make your decision that way.

Tony

Posted by Jeff Tenney

on Apr 18 2012 11:08 AM

Guru10795 points

Todd,

My guess is that nobody (not even TI engineers who visit this forum) will officially sanction the use of UART above 1MBaud.

But you are so close that it should work. Keep in mind that baud rates that high can fail with poor line transceivers, so hopefully you're not using transceivers and you are instead dealing with a TTL or logic-level interface.

One sticky point is the deglitch logic, which requires the bit to be at least 600ns. At 1.024MBaud, each bit is 976ns, so you just need to make sure the edges are clean and sharp.

And for receiving that data rate on MSP430, I'm guessing you plan on making friends with the DMA controller.

Jeff

Posted by Jens-Michael Gross

on Apr 18 2012 11:26 AM

Guru140610 points

Todd Anderson78572
The UART spec is 1 MBAUD. I have an application where the ideal BAUD rate is 1.024 MBAUD - how flexible is the spec in this regard?

The spec isn't flexible. This is why it is a spec. However, the UART may or may not work with a higher clock. There is no reason why it should work up to 1MBd, but at 1000001Bd it stops working.
However, up to 1MBd you can blame TI if it doesn't work. Above you're on your own. And the further you stray from the spec limit, the higher the chance that one or another (or all) MSPs will cease to function.

1.024MBd isn't that far, so chances are you'll never have problems with it. But be prepared that perhaps every now and then one MSP will refuse to do it. Mostly on the receiving direction, as this is the more fragile one.

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