• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 98 subscribers
  • Views 780 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

AM572X: Using UART in SYS/BIOS

AM5728: Baud rate differs between UART's

Kevin Stallard
Intellectual 445 points

Part Number: AM5728

Hi,

Both UART1 and UART3 are using the FUNC_48M_CLK.  I am using 0x1a in the baud rate low byte, 0 in the high byte.

UART3 has a bit time of around 8.6 usec, this translates to around 115k baud.  UART1 on the other hand has a bit time of around 8.8 translating to around 113k baud. 

The serial port receiving this data is tolerant of the 115k baud but is not able to handle data at 113k baud.

Why are the two UARTs demonstrating different bit times with the exact same settings?

Thanks

Kevin

  • 0
    TI__Guru**** 393215 points
    What software is this? Please provide complete details of the use case.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 445 points
    Bare metal code, a custom MLO. Again, setting up the UARTs exactly the same, same code (different base addresses).

    I am not sure what else I can add to further clarify. UART3 is transmitting at 115k baud, UART1 is transmitting at 113k baud. Both use the same clocks (48Mhz). Both have the same steps to activate their clocks (CM_L4PER_UART1_CLKCTRL and CM_L4PER_UART3_CLKCTRL).

    DPLL_PER appears to be setup correctly (UART3 works).

    Again, not sure what else I can add, let me know if there is something specific that would help.

    Thanks
    Kevin
  • 0 in reply to Biser Gatchev-XID
    Intellectual 445 points
    Let me ask you this Biser, are there any other timing registers, unique to the UARTs, that could affect TX bit timing? (on top of the UART baud rate registers and the M/N values of DPLL_PER?).

    I realize I have not filled up the space with a ton of information, I am just trying to keep it concise. If there is something that I am missing that would help get to the bottom of this, please help me understand what that is.

    Thanks,
    Kevin
  • 0 in reply to Biser Gatchev-XID
    Intellectual 445 points

    Okay, I am being a block-head.  I have been using a serial-USB converter that requires normal RS232 signal levels instead of a 3.3v TTL serial to USB converter.  Thanks for taking a look :)

    Kevin