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UART max speed

Altera_Forum
Honored Contributor II
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SOPC builder allows for "other" baud rate entries than the standard, with only throwing up a Warning. 

 

I need an isolated link between 2 Nios CPUs, and among other solutions, I'm looking at a 10Mbps isolated /RS-485 transceiver. The SOPC UART will allow me to set the baud rate this fast - but are there internal logic restrictions/constraints that anyone can think of?
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Altera_Forum
Honored Contributor II
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In Quartus II v6.0 Handbook -> embedded peripherals. 

You could find this for UART baudrate configuration : 

 

divisor=int((clok freq/baudrate)+0.5) 

baudrate = clock freq / (divisor +1) 

 

You have to determine max clock freq of your design to determine max baud rate 

 

 

How to modify baudrate : 

------------------------------- 

 

According to your clock freq and the baudrate you want, write into the divisor : 

 

IOWR_ALTERA_AVALON_UART_DIVISOR(uart_base_addr, new_divisor); 

 

don't forget to allow modification of divisor in SOPC Builder 

 

you can also read your divisor with IORD_ALTERA_AVALON_UART_DIVISOR.. 

You don't need to open a file descriptor on the uart IP device 

 

example : 

clock freq : 50Mhz 

baudrate : 921600 bds 

 

divisor = 54
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Altera_Forum
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Thanks for the reply, I was actually aware of the ability to divide the system clock down for derrivation of the baud rate, but I guess I am leary of whether I could really run Mbps with the uart in terms of processor performance. At 10Mbps, that would mean a byte interrupt every usec or so. Do you know if the processor can handle that? And I know it depends on what all else it is doing, what other interrupts it has to service, but in general?

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Altera_Forum
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