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Contributor
Contributor
3,199 Views
Registered: ‎01-02-2015

AXI UART 16550 receives continuous 0xFF bytes

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Device: xc7z030fbg676-2

 

I have a block diagram with two AXI UART 16550 ip cores. The AXI clock rate, which is being used for baud rate, is 100MHz. Both of these uarts appear to be hooked up to outside ports in the same way. In software, the same functions are used to configure, read, and write. However, both uarts do not both work the same way. uart0 continuously receives 0xFF bytes, whether it has anything being sent to it or not. If I do send data to it, I can see that data in the fifo, but behind all of the other 0xFFs. It transmits as expected. If I reduce the baud rate all the way down to 1200, uart0 works fine.

 

uart1 works correctly for baud rates between 1200 and 115200. 

 

Using chipscope, the baud rate produced appears to be what I expect. Also, I do not see any extra activity on the rx line that would cause false data to come through.

 

What could be causing this?

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Contributor
Contributor
5,824 Views
Registered: ‎01-02-2015

Re: AXI UART 16550 receives continuous 0xFF bytes

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This issue has been resolved. The problem was in hardware. A 12.5 MHz clock was coupling with the rx line. The reason this noise wasn't seen on chipscope is that this was the same clock being used to clock the ila.

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Teacher muzaffer
Teacher
3,152 Views
Registered: ‎03-31-2012

Re: AXI UART 16550 receives continuous 0xFF bytes

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@wdecook is your implementation timing clean?

- Please mark the Answer as "Accept as solution" if information provided is helpful.
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Contributor
Contributor
5,825 Views
Registered: ‎01-02-2015

Re: AXI UART 16550 receives continuous 0xFF bytes

Jump to solution

This issue has been resolved. The problem was in hardware. A 12.5 MHz clock was coupling with the rx line. The reason this noise wasn't seen on chipscope is that this was the same clock being used to clock the ila.

0 Kudos