TL16C752B: Error flag [7] of LSR

toshi-e2e

Hi all,
In Non FIFO mode, when reading the LSR after receiving data, usually the LSR value is 0x61.
However sometimes, the LSR value is 0xA1.
Why is LSR[7] set in spite of no error (PE, FE and Break)?

Regards,
Toshi

over 9 years ago

0 Francisco Javier Zamudio over 9 years ago

TI__Expert 5455 points

Hi Toshi

This device, in this mode, has an small problem with a timing anomaly. This problem only occurs under a special set of circumstances
(in non-FIFO mode) and can be worked around by using certain timing. When using the non-FIFO (single byte) mode of operation, it is
possible that valid data could be reported as available by either the line status register (LSR) or the interrupt identification
register (IIR), before the receiver holding register (RHR) can be read. For more detailed, you can check page 22 in datasheet.
Your current LSR status is:
61 01100001 THR and TSR empty|THR empty| Data in receiver
A1 10100001 Error in Rx FIFO| THR empty| Data in receiver
If you consider your current configuration, you are not work in FIFO mode, hence I would think that you would have A1 in LSR.

If possible, please Can you share your current configuration of registers?

Regards
Francisco

0 toshi-e2e over 9 years ago in reply to Francisco Javier Zamudio

Genius 4830 points

Hi, Francisco-san,
Thanks for your reply.
I would like to explain about my customer's condition when the error occurred.
Before getting 0xA1 of the LSR, FE or PE has occurred in succession.
And after that, the FIFO error of LSR is reset by resetting FCR [2-1].
Why is the FIFO error (LSR[7]) occurred in spite of Non-FIFO mode?

Current configuration of registers are as follows;

①IER= 0x7 ; RHR,THR and RXE are on
②IIR ; read only
③FCR=0x00 ; FIFO disable
④LCR=0x1B ; 8bit data + EP + 1ST
⑤MCR=0x08 ; Forces the INT(A-B) outputs to the active state
⑥SPR=0x00 ; default
⑦DLL=0x0A ; set Baud rate 125k
⑧DLH=0x00 ;
⑨EFR=default
⑩XON1 = default
⑪XON2 =default
⑫XOFF1=default
⑬XOFF2=default
⑭TCR =default
⑮TLR=default
⑯FIFOR=default

Thanks and regards,
Toshi

0 Francisco Javier Zamudio over 9 years ago in reply to toshi-e2e

TI__Expert 5455 points

Hi Toshi-san

I can see that your current configuration is right, but I recommend you that your customer makes a test following all steps in programmer's guide and set all registers values (all that you said default) as well. This part is important because when you don't set the values, the registers get other values. I also recommend you to take a look into the errata (www.ti.com/.../sllz049.pdf) that it mention with more detailed the problems with this device and the solutions. On the other hand, we have a new version of this device that I recommend you to use (www.ti.com/.../tl16c752d.pdf). In this version you won't have this kind of problems.
Please, make test and send me your feedback.

Best Regards
Francisco

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TL16C752B: Error flag [7] of LSR