UART receiver not ready

sanghavi — Wed, 30 Apr 2014 12:43:10 GMT

I am trying to enable UART receive interrupt using "UIMRn" register & “UCR”.

// Enable Serial Port 0 receiver event interrupt

CurrentUIMR |= MCF52xx_UART_UIMR_FFULL;

MCF52xx_UART0_UIMR = CurrentUIMR;

// Enable Serial Port 0 receiver.

MCF52xx_UART0_UCR = MCF52xx_UART_UCR_RX_ENABLED;

When I am reading UIMR & UISR contains, value is 0, in special condition (when I received noise on UnRXD line).

I encounter this issue in special condition, when I received noise (30 uS) signal on UnRXD line. In normal, condition my code is working as expected.

I am using MCF5275 processor.

Re: UART receiver not ready

TomE — Thu, 01 May 2014 06:02:37 GMT

> CurrentUIMR |= MCF52xx_UART_UIMR_FFULL;

That is only enabling interrupt on RxRDY (or FFULL if FFULL is set in UIMR, but don't do that).

Do you have any code to handle receive overruns? It will probably lock up if you don't.

"Table 27-5. USRn Field Descriptions" says "OE is cleared by the RESET ERROR STATUS command in UCRn."

> When I am reading UIMR & UISR contains, value is 0, in special condition (when I received noise on UnRXD line).

So your "special condition" is when you send a 30us pulse. Is it a clean test pulse 30us wide or higher frequency noise that long?

If the noise gave a Framing Error you should get a Receive Interrupt with FE. If it looks like a Break you might get RB or DB in UISR.

If "value is 0" means UISR is zero then there's no receive character or delta-break.

What are you expecting to happen when you send a 30us pulse? 30us is one bit or more at baud rates higher than 33,333 and a "Break" if faster than 300000, so it should look like a normal character.

What baud rate are you using? Positive or negative pulse?

Tom

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