Need help with LPC1767 Uart RX interrupt

Good Afternoon to all, I'm working with ARM processor LPC1768 in a MCB1700 board, and in my project i need to use uart to communicate with a PLC modem. I'm using the code bellow to do this. If a try to communicate with a Hyperterminal or similar on windows, my interruption works fine, but if a try to communicate with the before mentioned PLC modem, a can't get any interrupts. I have probed the uart pins P2.0 and P2.1 and the PLC modem pins, and i can see that my TX messages arrive on the modem, and i can see that the modem answer those messages accordingly, and i can see that the uart RX pin receives those messages, but no interruption are toggled...

Can anyone help me with this issue? any suggestion to other uart implementation?

//---------------------------------------------------------------------------
#include <LPC17xx.h>
#include "Serial.h"
//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
// Defines
//---------------------------------------------------------------------------
#define SW_FIFO_SIZE            512
#define RLS_INTERRUPT           0x03
#define RDA_INTERRUPT           0x02
#define CTI_INTERRUPT           0x06
#define THRE_INTERRUPT          0x01
#define LSR_RDR                 (1<<0)
#define LSR_OE                  (1<<1)
#define LSR_PE                  (1<<2)
#define LSR_FE                  (1<<3)
#define LSR_BI                  (1<<4)
#define LSR_THRE                (1<<5)
#define LSR_TEMT                (1<<6)
#define LSR_RXFE                (1<<7)
#define UART_DISABLED           0x00
#define UART_OPERATIONAL        0x01
#define UART_OVERFLOW           0x02
#define UART_PARITY_ERROR       0x03
#define UART_FRAMING_ERROR      0x04
#define UART_BREAK_DETECTED     0x05
#define UART_CHAR_TIMEOUT       0x06
//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
BYTE  UART0_RxBuf[UART0_RX_BUFFER_SIZE];
BYTE  UART0_TxBuf[UART0_RX_BUFFER_SIZE];
BYTE  UART0_RxTail;
BYTE  UART0_RxHead;
BYTE uart0_tx_sts;
BYTE uart0_rx_sts;
uint32_t rdaInterrupts = 0;
uint32_t ctiInterrupts = 0;
//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
// Controle
//---------------------------------------------------------------------------
void Serial0Init( unsigned int baudRate )
{
  int pclk, fdiv;

  LPC_SC->PCONP |= (1 << 3);
  LPC_PINCON->PINSEL0 |= (1 << 4);             /* Pin P0.2 used as TXD0 (Com0) */
  LPC_PINCON->PINSEL0 |= (1 << 6);             /* Pin P0.3 used as RXD0 (Com0) */

  LPC_SC->PCLKSEL0 &= ~(3 << 6); // clear bits
  LPC_SC->PCLKSEL0 |=  (1 << 6); // set to "01" (full speed)
  pclk = SystemCoreClock;

  LPC_UART0->LCR = 0x03;             /* 8 bits, no Parity, 1 Stop bit */
  LPC_UART0->LCR |= (1 << 7);
        /*
        fdiv = (pclk/(16*baudRate));
        LPC_UART0->DLM = (fdiv >> 8) & 0xFF;
        LPC_UART0->DLL = (fdiv) & 0xFF;
        */
  // baudrate of 38400 with a clock rate of 100 MHz
  LPC_UART0->DLM = 0;//Fdiv / 256;
  LPC_UART0->DLL = 108;//Fdiv % 256;
  LPC_UART0->FDR = 0x21;///

  LPC_UART0->LCR &= ~(1 << 7);
  LPC_UART0->FCR |= (0x0 << 6); //(0x3 = 14, 0x00 = 1)
  //LPC_UART0->FCR |= 0x01;
  //LPC_UART0->FCR |= 0x06;

  NVIC_EnableIRQ(UART0_IRQn);
  NVIC_SetPriority(UART0_IRQn,30);
  LPC_UART0->IER = 0x07; //Enable

  LPC_UART0->LCR    = 0x03;
}
//---------------------------------------------------------------------------
void UART0_IRQHandler(void) __irq
{
  BYTE intId, lsrReg;
  BYTE byData,bTmpTail;

  intId = ((LPC_UART0->IIR)>>1)& 0x7;
  if(intId == RLS_INTERRUPT) { //RLS
        lsrReg = LPC_UART0->LSR;
        if (lsrReg & LSR_OE)
                uart0_rx_sts = UART_OVERFLOW;
        else if (lsrReg & LSR_PE)
                uart0_rx_sts = UART_PARITY_ERROR;
        else if (lsrReg & LSR_FE)
                uart0_rx_sts = UART_FRAMING_ERROR;
        else if (lsrReg & LSR_BI)
                uart0_rx_sts = UART_BREAK_DETECTED;
  } else if (intId == RDA_INTERRUPT) {
    while((LPC_UART0->LSR) & 0x1) {
        UART0_RxBuf[UART0_RxHead] = LPC_UART0->RBR;
      UART0_RxHead += 1;
        if (UART0_RxHead == UART0_RX_BUFFER_SIZE)
        UART0_RxHead = 0;
    }
    rdaInterrupts++;
  } else if (intId == CTI_INTERRUPT) {
        while((LPC_UART0->LSR) & 0x1) {
        UART0_RxBuf[UART0_RxHead] = LPC_UART0->RBR;
      UART0_RxHead += 1;
        if (UART0_RxHead == UART0_RX_BUFFER_SIZE)
        UART0_RxHead = 0;
    }
    ctiInterrupts++;
  }
}
//---------------------------------------------------------------------------