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Hi! I set LPC2106 UART to work with 2 stop bits. After this I try to recieve few bytes transmitted with one stop bit, from PC computer to LPC2106. And, what is strange for me, LPC2106 UART returns only one, last byte from transmitted frame. I think, it is an error, becouse all chips compatible with 16c550, in this case return all bytes with no error indication (when second stop bit is missing). Am I right or not ? Regards Robert |
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LPC210x UART bug ?
Started by ●June 24, 2004
Reply by ●June 24, 20042004-06-24
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--- In , "hansklos2003" <hansklos2003@y...> wrote: > Hi! > > I set LPC2106 UART to work with 2 stop bits. After this I try to > recieve few bytes transmitted with one stop bit, from PC computer to > LPC2106. And, what is strange for me, LPC2106 UART returns only one, > last byte from transmitted frame. I think, it is an error, becouse > all chips compatible with 16c550, in this case return all bytes with > no error indication (when second stop bit is missing). > Am I right or not ? > > Regards > Robert Who said the LPC2106 was 16c550 compatible? A stop bit is the same as an idle line. Using 2 stop bits increases the idle time between characters. Many UARTS, when set for 2 stop bits put them on the transmission but do not bother to implement them on the reception (2 stop bits is always recievable by a UART set to 1 stop bit). If framing checks are fully implemented then a UART should not receive when there is only 1 stop bit. Having said that the UART in the LPC will always try and use a new edge as a start bit and so should recieve a successive character even if it causes a frame error in the previous character. Have you investigated frame errors? Are they being generated? |
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Reply by ●June 24, 20042004-06-24
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hansklos2003 wrote: > Hi! > > I set LPC2106 UART to work with 2 stop bits. After this I try to > recieve few bytes transmitted with one stop bit, from PC computer to > LPC2106. And, what is strange for me, LPC2106 UART returns only one, > last byte from transmitted frame. I think, it is an error, becouse > all chips compatible with 16c550, in this case return all bytes with > no error indication (when second stop bit is missing). > Am I right or not ? > > Regards > Robert > Hi Robert, if you send with one stop bit but the receiver expects two, the receiver generates a framing error only when the time between the stop bit of one byte and the start bit of the following byte is below one bit time. Ohterwise the idle state of the serial line will be interpreted as a stop bit. That's why your last byte is returned correctly. The description of the '16550 framing error bit says that in case the receiver sees a 0 when there should be a 1 for a stop bit it tries to resynchronize by assuming that 0 is the start bit of a following byte. Nevertheless, the error bit for the byte with the missing stop bit is set. The description of the LPC2106's UART say the same. Hence, every 16550 compatible UART should mark all but the last of your bytes erroneous. How do you return your bytes? Does the software on your LPC2106 evaluate the Line Status Register (LSR) when it reads a byte from the receiver register/FIFO? What does it do if LSR shows that there was a framing error in the byte you are going to read from the receiver register/FIFO? Regards, Jens |
Reply by ●June 24, 20042004-06-24
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> Who said the LPC2106 was 16c550 compatible? LPC210x datasheet : "Key features: ... Multiple serial interfaces including two UARTs (16C550) ..." I use interrupts to recieve bytes from Lpc210x UART. The problem is, this UART generate only one RDA interrupt, when last byte is recieved. There is no RLS interrupts - in means - UART does not signal framing errors. Earlier characters are lost with no error signalization... From my experience I know, other UARTs (for exapmle in AVR or '550 in PC) are ready to recieve next byte immediately after detecting first stop bit. Previous character is returned without framing error. Has someone similar problem ? Robert. |
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Reply by ●June 24, 20042004-06-24
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Robert If you are having problems with interrupt mode operation of the LPC uart, you might want to take a look at my code in the files section on Yahoo. http://groups.yahoo.com/group/lpc2000/files/ and look for the descriptive title of UT040311A.zip Regards -Bill Knight www.theARMPatch.com On Thu, 24 Jun 2004 16:10:59 -0000, hansklos2003 wrote: > Who said the LPC2106 was 16c550 compatible? LPC210x datasheet : "Key features: ... Multiple serial interfaces including two UARTs (16C550) ..." I use interrupts to recieve bytes from Lpc210x UART. The problem is, this UART generate only one RDA interrupt, when last byte is recieved. There is no RLS interrupts - in means - UART does not signal framing errors. Earlier characters are lost with no error signalization... From my experience I know, other UARTs (for exapmle in AVR or '550 in PC) are ready to recieve next byte immediately after detecting first stop bit. Previous character is returned without framing error. Has someone similar problem ? Robert. |
