シリアルインターフェイスIICAでデータを取得できません

static void R_MAIN_UserInit(void)
{
    /* Start user code. Do not edit comment generated here */
    EI();
    R_UART0_Start();

    buf[0]=0xF4;
    buf[1]=0x2E;
    buf[2]=0x00;
    R_IICA0_Master_Send(0xEE, (uint8_t *)buf, 2,20);
    sleep(20);
    while (1U){
        //R_UART0_Receive((uint8_t *)rx_buf,10);
     uart();
     sleep(10);
    }
    R_UART0_Stop();
    /* End user code. Do not edit comment generated here */
}

/* Start user code for adding. Do not edit comment generated here */
void uart(void){
    int i;
    R_IICA0_Master_Receive(0xEF, (uint8_t *)buf,256,20);
    for(i=0;i<256;i++){
     if((i%8)==7){
      sprintf_tiny(data,"%03d,%03d\n ",i,buf[i]);
     }else{
      sprintf_tiny(data,"%03d,%03d ",i,buf[i]);
     }
    //R_UART0_Send((uint8_t*)message,strlen(message));
    R_UART0_Send((uint8_t*)data,10);
    sleep(15);
   }
}