topic problem with uart0 and printf in mke06 in Kinetis Microcontrollers

problem with uart0 and printf in mke06

Iotelctronic — Wed, 11 Mar 2026 19:05:35 GMT

I have a PCB where I connect Bluetooth using UART0 with the MKE06Z128VQH4 MCU. First, I am doing communication tests using an FTDI adapter and the Hercules terminal.

I am using the UART example from the SDK that comes configured for UART1. I configured UART1 and used the example, and it worked well. However, I noticed that when it tries to use printf for debugging, the information arrives truncated in the Hercules terminal.

But that is not the main problem. The problem is that when I try the same example with UART0, it does not work. When I send information from Hercules, I can see that inside the while loop it enters the instruction to send data, which indicates that the information is received and the code attempts to send it. However, nothing appears in the Hercules terminal.

I disabled printf, but I still have the same problem.

Re: problem with uart0 and printf in mke06

Iotelctronic — Wed, 11 Mar 2026 19:58:25 GMT

my code is this:

#include "board.h" #include "fsl_uart.h" #include "pin_mux.h" #include <stdint.h> #include <stdbool.h> #define DEMO_UART UART0 #define DEMO_UART_CLK_FREQ CLOCK_GetFreq(kCLOCK_BusClk) #define DEMO_UART_IRQn UART0_IRQn #define DEMO_UART_IRQHandler UART0_IRQHandler #define RING_BUFFER_SIZE 16 uint8_t ringBuffer[RING_BUFFER_SIZE]; volatile uint16_t txIndex = 0; volatile uint16_t rxIndex = 0; void DEMO_UART_IRQHandler(void) { uint8_t data; if (kUART_RxDataRegFullFlag & UART_GetStatusFlags(DEMO_UART)) { data = UART_ReadByte(DEMO_UART); if (((rxIndex + 1) % RING_BUFFER_SIZE) != txIndex) { ringBuffer[rxIndex] = data; rxIndex = (rxIndex + 1) % RING_BUFFER_SIZE; } } SDK_ISR_EXIT_BARRIER; } int main(void) { BOARD_InitBootPins(); BOARD_InitBootClocks(); uart_config_t config; UART_GetDefaultConfig(&config); config.baudRate_Bps = 115200; config.enableTx = true; config.enableRx = true; UART_Init(DEMO_UART, &config, DEMO_UART_CLK_FREQ); // Mensaje de bienvenida por UART0 uint8_t welcome[] = "Sistema iniciado - Comunicacion con Hercules\r\n"; UART_WriteBlocking(DEMO_UART, welcome, sizeof(welcome)-1); UART_EnableInterrupts(DEMO_UART, kUART_RxDataRegFullInterruptEnable); EnableIRQ(DEMO_UART_IRQn); while (1) { // Eco de los datos recibidos if (rxIndex != txIndex) { UART_WriteByte(DEMO_UART, ringBuffer[txIndex]); txIndex = (txIndex + 1) % RING_BUFFER_SIZE; } } }

Re: problem with uart0 and printf in mke06

Alice_Yang — Thu, 12 Mar 2026 02:40:37 GMT

Hello @Iotelctronic

Please verify that the UART0‑TX pin on your board is properly configured in your software code, and ensure that the correct baud rate is selected in Hercules.

Alice

Re: problem with uart0 and printf in mke06

Iotelctronic — Thu, 12 Mar 2026 11:21:55 GMT

Hello! Thank you for your response. The pin configurations are in pin_mux.c as follows:

void BOARD_InitPins(void) { /* pin 48,47 is configured as UART0_RX, UART0_TX */ PORT_SetPinSelect(kPORT_UART0, kPORT_UART0_RXPTA2_TXPTA3); SIM->SOPT0 = ((SIM->SOPT0 & /* Mask bits to zero which are setting */ (~(SIM_SOPT0_RXDFE_MASK))) /* UART0 RxD Filter Select: RXD0 input signal is connected to UART0 module directly. */ | SIM_SOPT0_RXDFE(SOPT0_RXDFE_0b00)); }

in the configtool:

in the hercules have the correct baud:115200. i can view the data in the buffer rx, but the eco tx for hercules not. this case is with uart0, with uart1 is working well.