Lpc2000

I have the same problem with baudrates in lpc2138,
when running at 12 mhZ without pll, the baudrate that
i have reached 38400 max. At higher bauds there is no
response!
with pll higher bauds can be reached.

--- Karl Olsen <kro@...> wrote:

> ---- Original Message ----
> From: "Mauricio Scaff" <scaffm@...>
> To: <lpc2000@yahoogroups.com>
> Sent: Tuesday, January 17, 2006 10:25 PM
> Subject: [lpc2000] weird problem in UART
> 
> > I have the following problem that is very odd.
> >
> > I have a very simple program that waits one char
> from the uart0 and
> > sends it back to it.
> > If I set the baudrate to 57600, it works ok, but
> if I set the baud
> > rate to 115200, the host (PC)  understands any
> data I send, but the
> > LPC just gives Frame errors even if a single byte
> is sent.....
> > I'm using a LPC2146 @ 12Mhz
> > Using these constants in the baud rate generator
> should give an error
> > of 0,16%, and the transmission works... Why can't
> I receive data ?
> > Thanks, Mauricio
> >
> >
> > This is the code:
> >
> > void ser0_init(void)
> > {
> >  U0IER = 0;
> >  U0IIR;
> >  U0RBR;
> >  U0LSR;
> >
> >  U0LCR    = 0x83; // Enable access to divisor
> latchs
> >
> > // 57600 @ PERCLK = 12Mhz
> > //  U0DLL    = 13;
> > //  U0DLM    = 0;
> > //  U0FDR    = 1<<4|0; // MulVal[7..4] 
> DivAddVal[3..0]
> >
> > // 115200 @ PERCLK = 12Mhz
> >  U0DLL    = 1;
> >  U0DLM    = 0;
> >  U0FDR    = 2<<4|11; // MulVal[7..4] 
> DivAddVal[3..0]
> >
> >  U0LCR    = 0x03;  // 8n1
> >  U0FCR    = 0x87;  // FIFO enabled and cleared;
> Trigger @ 8 bytes
> > }
> > [...]
> 
> Others have had similar problems with the fractional
> baudrate generator and
> U0DLL=1, search the archive.
> 
> Philips has not documented how the fractional
> baudrate generator actually
> works, other than "This pre-scaler takes the VPB
> clock and generates an
> output clock per specified fractional requirements".
>  When U0DLL=1, this
> output clock is equal to the 16xbaud clock that is
> used when sampling the
> RxD signal.
> 
> My guess: If that pre-scaler doesn't spread the
> extra clocks that it inserts
> evenly enough, the RxD circuit might not sample the
> incoming bits correctly,
> and you get wrong bytes or framing errors.
> 
> philips_apps, are there any limitations of the
> fractional baudrate generator
> at high baudrates?
> 
> Karl Olsen
> 
> 


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