Rs485 problema de recepción en el microcontrolador Pic

Comencé a trabajar en Rs485 (Sp3485c) que está interconectado con el microcontrolador Pic24fj128ga202 IC. Este controlador tiene 4 uart's uno está conectado a la PC a través de max3232 ic, gps, gsm y otro para rs485.uart1,2,3 se ha configurado muy correctamente y puedo enviar y recibir datos a través de estos uarts, pero cuando envío datos a través del cuarto uart se transmiten los datos, verifiqué la transmisión a través de tx interrupt. Para verificar el propósito hice un microcontrolador como transmisor y otro mocricontroller como receptor, ambos controladores están conectados a través de RS485. El principal problema es que no recibo ningún dato en otro microcontrolador a través de rs485.

Aquí está el código del transmisor

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include<stdbool.h>

//#include "p24FJ128GA202.h"              // Pic24FJ128GA202 header file
#include "C:\Program     Files\Microchip\xc16\v1.24\support\PIC24F\h\p24FJ128GA202.h"
#include "uart.h"
#define PWRKEY    PORTBbits.RB12

// Function Prototypes
void InitProcessor(void);
void InitDelayms(void);
void Timer2Init(void);
void Delayms(uint16_t delay);

void __attribute__ ((interrupt,no_auto_psv)) _U4TXInterrupt(void) 
{ 
    uart1tx('O');
    IFS5bits.U4TXIF   = 0;  
} 

int main()
{
    unsigned int i=0;
    InitProcessor();
    Delayms(500);                                               // oscillator to get lock
    uart1str((unsigned char *)"\r\nRs485 Transmitter\r\n");
    while(1)
    {
        uart4tx('T');
        Delayms(3000);
    }
    return 0;
}

void InitProcessor(void)
{
    // Oscillator
    OSCCON = 0x0011;
    CLKDIV = 0x0000; 

//PPS for UART1
RPINR18bits.U1RXR   = 7;   //UART1 receive set to RB7
RPOR4bits.RP8R      = 3;   //UART1 transmit set to RB8

//PPS for UART2
RPINR19bits.U2RXR   = 14;  // uart2 receive set to RB14
RPOR6bits.RP13R     = 5;   //UART2 transmit set to RB13
//PPS for UART4
RPINR27bits.U4RXR   = 4;  // uart4 RX
RPOR3bits.RP6R      = 21;   //UART4 

// Configure Digital pins
ANSA = 0x0003;
ANSB = 0x0000;

//  Assign  IO values for Ports
PORTA = 0x0000;
TRISA = 0x001B;
TRISB = 0x469f;                   // 7 as receive and 8 as transmitter
//PORTB = 0x0000;

// Init UART1
U1MODE = 0x0000;
U1STA = 0x0000;                   //Enable Transmission, Clear all flags
U1BRG = 103;//25;9600
U1MODEbits.UARTEN = 1;            // And turn the peripheral on
U1STAbits.UTXEN = 1;

// Init UART2
U2MODE = 0x0000;
U2STA  = 0x0000;                  //Enable Transmission, Clear all flags
U2BRG  = 103;
U2MODEbits.UARTEN = 1;            // And turn the peripheral on
U2STAbits.UTXEN = 1;

U4MODE = 0x0000;
U4STA  = 0x0000;                  //Enable Transmission, Clear all flags
U4BRG  = 103;
IFS5bits.U4TXIF   = 0;  
IEC5bits.U4TXIE   = 1;
U4MODEbits.UARTEN = 1;            // And turn the peripheral on
U4STAbits.UTXEN = 1;

// Interrupt Bits 
INTCON1 = 0x0000;                                               // Disable  Interrupts
INTCON2 = 0x0000;


InitDelayms();
PWRKEY = 1;
Delayms(1000);
}

void InitDelayms(void)
{
    // T1 - Clk Source: Fosc/2 (Fcyc)
    T1CONbits.TCS = 0;
    // T1 - Pre scale: 1:1 (4MHz / 250nS per tick)
    T1CONbits.TCKPS = 0;
    // PR1 adjusted to account for sw delays intro'd in loop below at 16MHz
    PR1 = 16000;
    // Clear TMR1
    TMR1 = 0;
    // Reset T1IF
    IFS0bits.T1IF = 0;
    // T1 - Turn on
    T1CONbits.TON = 1;
}
void Delayms(uint16_t delay)
{
    // basic kernel is 1mS (32 ticks @ 31.25uS/tick)

    while(delay>0)
    {
        // Clear TMR1
        TMR1 = 0;
        // Reset T1IF
        IFS0bits.T1IF = 0;
        // Wait 1mS
        while(!IFS0bits.T1IF);
        delay--;
    }

}

que transmite datos por cada 3 segundos. Código del receptor

    #include <stdio.h>
    #include <stdint.h>
    #include <string.h>
    #include <math.h>
    #include<stdbool.h>

    //#include "p24FJ128GA202.h"              // Pic24FJ128GA202 header file
    #include "C:\Program Files\Microchip\xc16\v1.24\support\PIC24F\h\p24FJ128GA202.h"
    #include "uart.h"
    #define PWRKEY    PORTBbits.RB12

    // Function Prototypes
    void InitProcessor(void);
    void InitDelayms(void);
    void Timer2Init(void);
    void Delayms(uint16_t delay);
    void __attribute__ ((interrupt,no_auto_psv)) _U4RXInterrupt(void)
    {
        uart1tx(uart4rx());
        IFS5bits.U4RXIF   = 0;       
    }

    int main()
    {
        unsigned int i=0;
        InitProcessor();
        Delayms(500);                                               // oscillator to get lock
        uart1str((unsigned char *)"\r\nRs485 with Modbus Protocol\r\n");
        Rs485Re_De=0;    // receiver
        while(1)
        {
            Delayms(1000);
        }
        return 0;
    }

    void InitProcessor(void)
    {
        // Oscillator
        OSCCON = 0x0011;
        CLKDIV = 0x0000; 

        //PPS for UART1
        RPINR18bits.U1RXR   = 7;   //UART1 receive set to RB7
        RPOR4bits.RP8R      = 3;   //UART1 transmit set to RB8

        //PPS for UART2
        RPINR19bits.U2RXR   = 14;  // uart2 receive set to RB14
        RPOR6bits.RP13R     = 5;   //UART2 transmit set to RB13
        //PPS for UART4
        RPINR27bits.U4RXR   = 4;  // uart4 RX
        RPOR3bits.RP6R      = 21;   //UART4 

        // Configure Digital pins
        ANSA = 0x0003;
        ANSB = 0x0000;

        //  Assign  IO values for Ports
        PORTA = 0x0000;
        TRISA = 0x001B;
        TRISB = 0x469f;                   // 7 as receive and 8 as transmitter
        //PORTB = 0x0000;

        // Init UART1
        U1MODE = 0x0000;
        U1STA = 0x0000;                   //Enable Transmission, Clear all flags
        U1BRG = 103;//25;9600
        U1MODEbits.UARTEN = 1;            // And turn the peripheral on
        U1STAbits.UTXEN = 1;

        // Init UART2
        U2MODE = 0x0000;
        U2STA  = 0x0000;                  //Enable Transmission, Clear all flags
        U2BRG  = 103;
        U2MODEbits.UARTEN = 1;            // And turn the peripheral on
        U2STAbits.UTXEN = 1;

        U4MODE = 0x0000;
        U4STA  = 0x0000;                  //Enable Transmission, Clear all flags
        U4BRG  = 103;
        IFS5bits.U4RXIF   = 0;            // Clear the Receive Interrupt Flag
        IEC5bits.U4RXIE   = 1;            // Enable Receive Interrupts
        U4MODEbits.UARTEN = 1;            // And turn the peripheral on
        U4STAbits.UTXEN = 1;

        // Interrupt Bits 
        INTCON1 = 0x0000;                                               // Disable  Interrupts
        INTCON2 = 0x0000;


        InitDelayms();
        PWRKEY = 1;
        Delayms(1000);
    }

    void InitDelayms(void)
    {
        // T1 - Clk Source: Fosc/2 (Fcyc)
        T1CONbits.TCS = 0;
        // T1 - Pre scale: 1:1 (4MHz / 250nS per tick)
        T1CONbits.TCKPS = 0;
        // PR1 adjusted to account for sw delays intro'd in loop below at 16MHz
        PR1 = 16000;
        // Clear TMR1
        TMR1 = 0;
        // Reset T1IF
        IFS0bits.T1IF = 0;
        // T1 - Turn on
        T1CONbits.TON = 1;
    }
    void Delayms(uint16_t delay)
    {
        // basic kernel is 1mS (32 ticks @ 31.25uS/tick)

        while(delay>0)
        {
            // Clear TMR1
            TMR1 = 0;
            // Reset T1IF
            IFS0bits.T1IF = 0;
            // Wait 1mS
            while(!IFS0bits.T1IF);
            delay--;
        }

    }

He escrito una función de interrupción para el receptor que imprime los datos en la recepción, el problema está aquí donde no obtengo ningún dato

Diagrama de conexión Pic to PIC Pic1 A - Pic2 A Pic1 B - Pic2 B Pic1 Gnd - Pic2 Gnd respectivamente.

Pic2 uart1 a max 3232 a pc para ver la salida.

estos son el PIC, RS485, diagrama de salida respectivamente.