diff --git a/Core/Src/main.c b/Core/Src/main.c
index d604566..62d12fb 100644
--- a/Core/Src/main.c
+++ b/Core/Src/main.c
@@ -24,6 +24,7 @@
 #include "printf.h"
 #include <usart2_it.h>
 #include <usart6_it.h>
+#include "usart1_it.h"
 /* USER CODE END Includes */
 
 /* Private typedef -----------------------------------------------------------*/
@@ -111,6 +112,7 @@ int main(void) {
 
    Usart2_Init();
    Usart6_Init();
+   Usart1_Init();
    init_printf(NULL, &uart_putc);// connect printf to UART
    printf("Hello world. This is a Nucleo UART and printf sample with IRQ and ring buffer.\n");
    /* USER CODE END 2 */
diff --git a/Core/user/usart1_it.c b/Core/user/usart1_it.c
new file mode 100644
index 0000000..060f4c4
--- /dev/null
+++ b/Core/user/usart1_it.c
@@ -0,0 +1,141 @@
+/***************************************************************************//**
+* @file  usart1_it.c
+* @brief UART with interrupt and ring buffer (USART1)
+*//****************************************************************************/
+
+#include "stm32f4xx_hal.h"
+//------------------------------C library---------------------------------------
+#include <stdlib.h>
+//----------------------------user includes-------------------------------------
+#include "usart1_it.h"
+#include "usart1_it_cfg.h"
+//------------------------------------------------------------------------------
+
+
+
+
+/* Private typedefs ----------------------------------------------------------*/
+
+/* Private macros ------------------------------------------------------------*/
+
+//====== UART buffer defines ===================================================
+#define  USART1_RXBUF_MASK    (USART1_RXBUF_SIZE - 1)
+#define  USART1_TXBUF_MASK    (USART1_TXBUF_SIZE - 1)
+
+#if ( USART1_RXBUF_SIZE & USART1_RXBUF_MASK )
+#error RX buffer size is not a power of 2!
+#endif
+
+#if ( USART1_TXBUF_SIZE & USART1_TXBUF_MASK )
+#error TX buffer size is not a power of 2!
+#endif
+
+
+/* Private variables ---------------------------------------------------------*/
+
+//====== Variables for transmitter =============================================
+static          uint8_t  Usart1TxBuf[USART1_TXBUF_SIZE];
+static          uint16_t Usart1TxWrIdx = 0;
+static volatile uint16_t Usart1TxRdIdx = 0;
+
+//====== Variables for Receiver ================================================
+static          uint8_t  Usart1RxBuf[USART1_RXBUF_SIZE];
+static volatile uint16_t Usart1RxWrIdx = 0;
+static volatile uint16_t Usart1RxRdIdx = 0;
+
+
+/* Public variables ----------------------------------------------------------*/
+
+
+/* Functions -----------------------------------------------------------------*/
+
+
+/***************************************************************************//**
+* @brief  USART1 init
+*//****************************************************************************/
+void Usart1_Init(void) {
+   USART1->CR1 |= USART_CR1_RXNEIE; // Enable RX interrupt
+}
+
+
+/***************************************************************************//**
+* @brief  USART1 interrupt handler
+*//****************************************************************************/
+void USART1_IRQHandler(void) {
+   uint32_t statusreg = USART1->SR;                      // read interrupt flags
+
+   if ((statusreg & USART_SR_RXNE)) {                    // RX interrupt
+      uint8_t d = USART1->DR;                            // read received byte
+      uint_fast16_t wr = Usart1RxWrIdx;
+      wr = (wr + 1) & USART1_RXBUF_MASK;                 // new write index
+      Usart1RxBuf[wr] = d;                               // received data to buffer
+      Usart1RxWrIdx = wr;                                // Store new index
+   }
+
+   if ((statusreg & USART_SR_TXE)) {                     // TX interrupt
+      uint_fast16_t rd = Usart1TxRdIdx;
+      uint_fast16_t wr = Usart1TxWrIdx;
+      if (wr != rd) {                                    // data in buffer
+         rd = (rd + 1) & USART1_TXBUF_MASK;              // new read index
+         USART1->DR = Usart1TxBuf[rd];                   // send data byte
+         Usart1TxRdIdx = rd;                             // Store new index
+      }
+      if (wr == rd) {                                    // data buffer empty
+         USART1->CR1 &= ~USART_CR1_TXEIE;                // INT disable
+      }
+   }
+}
+
+
+/***************************************************************************//**
+* @brief  Send byte to UART
+* @param  d: byte to send
+*//****************************************************************************/
+void Usart1_PutByte(uint8_t d) {
+   uint_fast16_t wr = Usart1TxWrIdx;
+   wr = (wr + 1) & USART1_TXBUF_MASK;     // new write index
+   if (wr == Usart1TxRdIdx) {             // No free space in buffer (overflow)
+      return;                             // drop remaining data (Attention! Buffer overflow not signaled! Use bigger buffer)
+   }
+   Usart1TxBuf[wr] = d;                   // Store data in buffer
+   Usart1TxWrIdx = wr;                    // Store new index
+   USART1->CR1 |= USART_CR1_TXEIE;        // Interrupt enable (start send)
+}
+
+
+/***************************************************************************//**
+* @brief  Send more data to UART
+* @param  src: data to send
+* @param  n:   count of data
+*//****************************************************************************/
+void Usart1_PutData (void* src, uint16_t n) {
+   uint8_t* p = src;
+   uint_fast16_t wr = Usart1TxWrIdx;
+   while (n) {
+      wr = (wr + 1) & USART1_TXBUF_MASK;  // new write index
+      if (wr == Usart1TxRdIdx) {          // No free space in buffer (overflow)
+         break;                           // drop remaining data (Attention! Buffer overflow not signaled! Use bigger buffer)
+      }
+      Usart1TxBuf[wr] = *p;               // Store data in buffer
+      p++;
+      n--;
+   }
+   Usart1TxWrIdx = wr;                    // Store new index
+   USART1->CR1 |= USART_CR1_TXEIE;        // Interrupt enable (start send)
+}
+
+/***************************************************************************//**
+* @brief  Read data from UART RX buffer
+* @return received character, -1: no data in RX buffer
+*//****************************************************************************/
+int16_t Usart1_GetByte(void) {
+   uint_fast16_t rd = Usart1RxRdIdx;
+   if (rd != Usart1RxWrIdx) {             // new data in buffer
+      rd = (rd + 1) & USART1_RXBUF_MASK;  // new read index
+      Usart1RxRdIdx = rd;                 // store new index
+      return Usart1RxBuf[rd];             // return with data
+   }else {
+      return -1;                          // buffer empty
+   }
+}
+
diff --git a/Core/user/usart1_it.h b/Core/user/usart1_it.h
new file mode 100644
index 0000000..47d02a2
--- /dev/null
+++ b/Core/user/usart1_it.h
@@ -0,0 +1,13 @@
+// filepath: c:\projects\STM32CubeIDE\GNSS_Nucleo\Core\user\usart1_it.h
+#ifndef  __USART1_IT_H__
+#define  __USART1_IT_H__
+
+#include <stdint.h>
+
+extern void     Usart1_Init(void);
+extern void     Usart1_PutByte(uint8_t d);
+extern void     Usart1_PutData(void* src, uint16_t n);
+extern int16_t  Usart1_GetByte(void);
+
+
+#endif
diff --git a/Core/user/usart1_it_cfg.h b/Core/user/usart1_it_cfg.h
new file mode 100644
index 0000000..4bd5715
--- /dev/null
+++ b/Core/user/usart1_it_cfg.h
@@ -0,0 +1,8 @@
+// filepath: c:\projects\STM32CubeIDE\GNSS_Nucleo\Core\user\usart1_it_cfg.h
+#ifndef __USART1_IT_CFG_H__
+#define __USART1_IT_CFG_H__
+
+#define  USART1_RXBUF_SIZE          1024
+#define  USART1_TXBUF_SIZE          1024
+
+#endif // __USART1_IT_CFG_H__