Lpc2000

The baud rate may be off by 1.7 %, however the PC still communicated
correctly when I used the exact same baud rate, 117187, from other
register configurations (as reported U1DLL= 0x02, 0x03).  

Furthermore, the behavior of the receiver not working when U1DLL=0x01
is consistent with screwy behavior I got at 500000 baud.  I reported
on that in posting # 9985.

I have worked around my issue by doubling the PCLK (it was going at
1/4 CCLK) and using a U1DLL=0x02.  In this particular case it doesn't
seem to cause too many additional issues.  Regardless, the phenomenon
seems like an error in intended operation.

JP

--- In lpc2000@yahoogroups.com, "rtstofer" <rstofer@p...> wrote:
>
> 
> You baud rate error is on the order of 1.7%.  That the PC will 
> accept it is to its credit.  That the LPC won't is not a surprise.  
> Assuming your PCLK is as accurate as you hope - have you checked it 
> with a frequency counter?
> 
> The examples in the user manual have errors around 0.06%
> 
> Further, you may not be sending EXACTLY 115200 from the PC.
> 
> This is not to say I have any idea about how to resolve the issue.  
> I just noted the huge difference in % error versus the user manual.
> 
> Richard
> 
> 
> 
> --- In lpc2000@yahoogroups.com, "jp_thrower" <jp_thrower@y...> wrote:
> >
> > This post is a followup to my original post number 9985.
> > 
> > When U1DLL = 0x01, U1DLM=0x00, and is used with the fractional 
> divisor
> > U1FDR to set the baudrate, the device properly transmits at the
> > assigned baudrate, but does not receive at the assigned baudrate.
> > 
> > I have conducted a series of elementary tests using the frequency
> > 117187 and a PC com port terminal set to 115200 baud.  The program
> > (genesis from Keil's example to give credit) transmits characters 
> from
> > the LPC2148 to the PC, reads characters from the PC, and echos them
> > back to the PC.
> > 
> > The frequency 117187 can be acquired with multiple settings using 
> a 12
> > MHz clock, or 15 MHz PCLK:
> > 
> > UART_baudrate = PCLK/(16*(16*U1DLM+U1DLL)) * (MulVal/
> (MulVal+DivAddVal))
> > 
> > U1DLL, MulVal, DivAddVal, Equation
> > 0x01    0x1        0x7    117187 = 15000000/16/(1)*(1/8)
> > 0x02    0x1        0x3    117187 = 15000000/16/(2)*(1/4)
> > 0x03    0x9        0xF    117187 = 15000000/16/(3)*(9/24)
> > 
> > In each case, the tranmit of characters worked fine, but in the 
> case
> > of 0x01, the receive characters were garbled.
> > 
> > I do have set U1FCR |= 0x01, which the manual says is required for
> > correct operation.
> > 
> > Is there an errata on this?  Does UART0 have the same issue?
> > Is there a way around this that I don't know?
> > This is important to me because I have to work with 500000 baud
> > signal, and U1DLL=1 seems like my only option without swapping 
> crystals.
> > 
> > JP
> >
>