Lpc2000

jp_thrower wrote:

>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).  
>
>  
>
I thought that the acceptable degree of error is somewhere around 0.5%?  
1.7% seems to be very high...

Let's see, 2400 - 1.7% == 2359buad, nope, I would not expect that to 
work!  I've gotten errors while being as much as 10 points of at 2400, 
e.g. 2390baud.

Where do you see that a 1.7% deviation is acceptable?  It has been a 
while since I've played with software uarts but I tried to keep within 
0.25% of error.


TomW


>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
>>>
>>>      
>>>
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-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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