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Not able to use UART4 on LPC1778

Question asked by Vijay Vaidya on Jun 30, 2020
Latest reply on Jul 10, 2020 by Vijay Vaidya



On our new board we have wired up UART4 on Pins P5[3]-U4_RXD & P5[4]-U4_TXD.


We are also using UART0 and UART2 on the same board.

Our programs are based on LPCOpen2.10 libraries.

We have followed the same initialization steps in UART4 as those of UART0 & UART2.

The performance of UART0 & UART2 is as expected.


It is observed that after bytes are loaded to U4THR, No waveform is seen on U4_TXD pin.

For the testing, we have followed these steps,

1. The program is reduced to just 4 steps consisting of,

      i) Initialization of above mentioned pins in their respective functions (IOCON_FUNC4)

      ii) Initialize UART4 to 9600:8:N:1
      iii) Enable Transmitter by loading 0x1 to LPC_UART4->TER2
           Though actually this is not required, as at Reset, Transmitter is already Enabled
      iv) Load a byte 0x55 every about 50msec through a pure for loop delay


We don't observe any activity on U4_TXD Pin.


Our doubts are,

1. Since UART4 on LPC1778 is different than other UARTs', in that, it also supports Synchronous Mode as well as    Smart Card Mode,

   Does it require something more in Initialization


2. While digging on the net we could locate following thread,


      this thread seems to be really not resolved


3. As mentioned therein, we don't find TER register in the referred User Manual viz. UM10470.pdf Rev. 4.0 — 21    December 2016


But our doubt is, there is something missing in the initialization itself, as on Reset, Transmitter being Enabled,

it is bare minimum that we should see some activity on U4_TXD pin in the above mentioned steps.


We are stuck and not able to go ahead.


Any pointers on above will be highly appreciated.


Thank you very much,

- Vijay Vaidya