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RDM General Implementation Discussion General Discussion and questions relating to implementing RDM in a product.

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Old January 10th, 2016   #1
Cyril
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Default Frequence min responder

Hi

Someone can discuss about the minimal frequence necessary for the mcu ? I code a rdm responder fully fonctionnal but I have to work in 16 MHz but I don't understand why it don't work with 8MHz ...

Thank you

Have a nice day
Cyril
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Old January 10th, 2016   #2
hamish
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Default 485 IO Interrupt driven buffering

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Originally Posted by Cyril View Post
Hi

Someone can discuss about the minimal frequence necessary for the mcu ? I code a rdm responder fully fonctionnal but I have to work in 16 MHz but I don't understand why it don't work with 8MHz ...

Thank you

Have a nice day
Cyril
Hi Cyril

Two main factors that determine what clock speed is required to meet the requirements of RDM.

First, IMO, set up interrupt tasks for buffering IO/485 data, thus allowing you to run other processes without missing packet data.
Built in to these interrupt driven task should be the response timing to meet the responder requirements of the standard.

Second, consider how to handle your responses when saving data to non volatile memory. Either you will have to assign the data saving to another task and then respond ahead of the save task completing.
or
Alternatively, (not my preferred answer) employ ACK timer to allow time for the data save to complete before completing a response.

I have a myriad of responder implementations running on an 8MHZ clock, running several other processes with ample resource.

Hope this helps.

Hamish
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Old January 11th, 2016   #3
ericthegeek
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Originally Posted by Cyril View Post
Someone can discuss about the minimal frequence necessary for the mcu ? I code a rdm responder fully fonctionnal but I have to work in 16 MHz but I don't understand why it don't work with 8MHz ...
The only hard requirement is that whatever clocking architecture you use, it must be able to run the UART at 250 Kbits/second. UARTs vary, but typically need a clock at 16x or 32x the baud rate.

Beyond that, it depends on the CPU, and how efficient your software is. MHz is really meaningless as an indicator of processor performance.

Last edited by ericthegeek; January 13th, 2016 at 10:06 AM. Reason: Typo: "meaningless as an indicator" instead of "meaningless and an indicator"
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Old January 13th, 2016   #4
Cyril
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Thank you a lot for your advices.
Cyril
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