Max UART Baurate [LPC4357]

[lpcware]

Content originally posted in LPCWare by hlsa on Sat Jan 25 07:56:12 MST 2014
Using two LPC4357 I would like to establish a DMA based USART connection between them for high speed data transfer. This means data transfer should be as fast as possible. Unfortunately there is no clear statement in the datasheet or user manual about the maximum baudrate.

The only information I found is the typical USART clock cycle time of 0.1 µs. This would mean, that the maximum speed is 10,000,000 Bits/s.
Using "no parity" and "one stopbit", the transfer of one byte needs 10 Bits. Thus the maximum speed equals 1,000,000 Bytes/s.


Can anyone from NXP confirm this?


Best regards,
Holger

[lpcware]

Content originally posted in LPCWare by hlsa on Wed Feb 05 00:04:52 MST 2014
Thanks for your response!

Again I had a look at the data sheet. By searching for "8" (*ughh*) I found the information in the functional description (chapter 7.19).
However, usually such information is provided in dynamic characteristics (chapter 11.9). Here this information is missing.

Best regards,
Holger

[lpcware]

Content originally posted in LPCWare by drs on Tue Feb 04 12:04:21 MST 2014
The data sheet shows 8MBit/s

[lpcware]

Content originally posted in LPCWare by hlsa on Wed Jan 29 01:29:29 MST 2014
Thank you very much for your answers. However, they have not been very helpful to me.

@rocketdawg:
I have recognized the formula in the users manual. But according to it, a baudrate which is higher than 10,000,000 Bits/s is possible. It is for example possible to calculate register values, which allow 11,000,000 Bits/s and I already had this working in the lab. But this only tells me, that I can set the registers accordingly. This does not tell me, whether this speed is within the specified range.

@drs:
USB is pretty good stuff for consumer applications. However, I do have an industrial application and because of the rough EMC environment, my data transfer needs to be done on an RS485 bus. USB is a "nogo" for such industrial applications.
@rocketdawg:
USB cables are standardized for consumer applications. Here they do neither need to fulfill any IP protection class nor are any screw type connectors required. In professional industrial applications, and so in mine, this is the case.

So my question is still open and I still hope for an answer:
What is the maximum specified UART speed?

Best regards,
Holger

[lpcware]

Content originally posted in LPCWare by rocketdawg on Tue Jan 28 09:32:54 MST 2014

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Quote: drs
Have you considered using USB to transfer data between your two boards? You should be able to get close to 40mbytes/sec and that's with built-in throttling and error detection/retry.

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good point.  Also the cable and connectors are standard

[lpcware]

Content originally posted in LPCWare by drs on Mon Jan 27 23:49:33 MST 2014
Have you considered using USB to transfer data between your two boards? You should be able to get close to 40mbytes/sec and that's with built-in throttling and error detection/retry.

[lpcware]

Content originally posted in LPCWare by rocketdawg on Mon Jan 27 09:57:18 MST 2014
well i come up with something different if I look at UM10503 Rev 1.7
section 39.6.12
there is a nice formula.
about half of your guess.
Since both sides are 4357, there is no need for baud rate error calculation, but you might want to verify that crystal tolerance does not create a large mismatch.
the reference manual does contain the information you need.

SPI might be faster