SPI communication between two PICs

Hi!
I am trying to transfer data from master to slave and from slave to master at the same time. I have tried to use SPI for the communication. I cannot go for USART or I2C because I have to use those pins for other configuration. So, I am left only with SPI. I have used MPLab and C18 compiler. I have posted the code below. In the program I have tried to send character 'B' from master to slave and character 'Z' from slave to master. When I run the program, I can see 'B' is sent from the master and received by the slave. But character 'Z' is lost somewhere. I guess, I am not good in configuration and communication algorithm. I have used PIC-18F4550. So, please help me out!! Thank you in advance!!

Master code
#include <htc.h>
#define _XTAL_FREQ 48000000

//config word(s)
#pragma config PLLDIV = 5, CPUDIV = OSC1_PLL2, USBDIV = 2 //20MHz XTAL/ '5' -> 96MHz PLL/' 2'= 48MHz CPU + USB
#pragma config IESO = OFF, FOSC = HSPLL_HS, FCMEN = OFF //Internal Osc off, HS Xtal, failsafe clock monitoring on
#pragma config VREGEN = ON, BOR = OFF, BORV = 0, PWRT = ON //usb vreg on, BORDIS, PWRTEN
#pragma config WDTPS = 32768, WDT = OFF //WDTDIS
#pragma config CCP2MX = ON, PBADEN = OFF, LPT1OSC = OFF, MCLRE = ON //CCP2:RC0, PortB Digital on reset, timer1 highpower, MCLREN
#pragma config DEBUG = OFF, STVREN = ON, XINST = OFF, LVP = OFF, ICPRT = OFF //debug mode off, stack error reset on, xtended instructions off, LVPDIS
#pragma config CP0 = OFF, CP1 = OFF, CP2 = OFF, CP3 = OFF //CODE PROTECT OFF
#pragma config CPD = OFF, CPB = OFF
#pragma config WRT0 = OFF, WRT1 = OFF, WRT2 = OFF, WRT3 = OFF
#pragma config WRTB = OFF, WRTC = OFF, WRTD = OFF
#pragma config EBTR0 = OFF, EBTR1 = OFF, EBTR2 = OFF, EBTR3 = OFF
#pragma config EBTRB = OFF

#define SS RC5 //this pin when low selects the slave
char a;

void SPI_enable()
{
//SSPSTAT=0xC0;
SMP=1; //Input data sampled at the end of data o/p time
CKE=1; //Transmission at transition from active to ideal

//SSPCON1=0x20;
WCOL=0; //No collision
CKP=0; // Ideal state is low level
SSPEN=1; //Enable serial port
SSPM3=SSPM2=SSPM1=SSPM0=0; // Master Mode, Fosc/4 clock for data transfer
}

void SPI_read()
{
SS=0; //select slave
SSPIF=0;
SSPBUF='B';
while(!BF);
while(!SSPIF);
a=SSPBUF;
SSPIF=0;
SS=1;
}

int main()
{
//Port initialization
TRISA=0x00; //RA5 as output
TRISB=0b11111101; //making RB1 as output and other as input
TRISC=0x00; //making all pins as output

//Configuration of interrupt

SPI_enable(); // enables SPI module
SPI_read();
while(1)
{
SPI_read();
}
}

Slave Code
#include <htc.h>

#define _XTAL_FREQ 48000000

//config word(s)
#pragma config PLLDIV = 5, CPUDIV = OSC1_PLL2, USBDIV = 2 //20MHz XTAL/ '5' -> 96MHz PLL/' 2'= 48MHz CPU + USB
#pragma config IESO = OFF, FOSC = HSPLL_HS, FCMEN = OFF //Internal Osc off, HS Xtal, failsafe clock monitoring on
#pragma config VREGEN = ON, BOR = OFF, BORV = 0, PWRT = ON //usb vreg on, BORDIS, PWRTEN
#pragma config WDTPS = 32768, WDT = OFF //WDTDIS
#pragma config CCP2MX = ON, PBADEN = OFF, LPT1OSC = OFF, MCLRE = ON //CCP2:RC0, PortB Digital on reset, timer1 highpower, MCLREN
#pragma config DEBUG = OFF, STVREN = ON, XINST = OFF, LVP = OFF, ICPRT = OFF //debug mode off, stack error reset on, xtended instructions off, LVPDIS
#pragma config CP0 = OFF, CP1 = OFF, CP2 = OFF, CP3 = OFF //CODE PROTECT OFF
#pragma config CPD = OFF, CPB = OFF
#pragma config WRT0 = OFF, WRT1 = OFF, WRT2 = OFF, WRT3 = OFF
#pragma config WRTB = OFF, WRTC = OFF, WRTD = OFF
#pragma config EBTR0 = OFF, EBTR1 = OFF, EBTR2 = OFF, EBTR3 = OFF
#pragma config EBTRB = OFF

char a;
void SPI_enable()
{
//SSPSTAT=0xC0;
SMP=0; //must be cleared for slave mode
CKE=1; //Transmission at transition from active to ideal


//SSPCON1=0x20;
WCOL=0; //No collision
CKP=0; // Ideal state is low level
SSPEN=1; //Slave mode
SSPM3=0;SSPM2=1;SSPM1=0;SSPM0=0; //SPI Slave mode, SCK clock, SS control bit enabled
}

void SPI_write()
{

//.......TRANSFER DATA.......
SSPIF=0;
SSPBUF='Z';
while(!BF); //Transfer complete
while(!SSPIF);
a=SSPBUF;
SSPIF=0;
}

void main()
{
TRISA=0xFF; //Port A as input
TRISB=0xFF; //Port B as input
TRISC=0x00; //Port C as output
SPI_enable(); //Enable SPI in slave mode
SPI_write();
while(1)
{
}
}

Hello there,


please go through these links.

http://www.pyroelectro.com/tutorials/spi_master_slave/software.html

https://www.edaboard.com/threads/149997/

https://www.edaboard.com/threads/261292/

Best regards,
www.youtube.com/watch?v=MPMzgJyeVpM

https://www.edaboard.com/threads/256734/

http://e2e.ti.com/support/microcontrollers/msp430/f/166/t/179056.aspx

http://www.microchip.com/forums/m649609.aspx

http://ww1.microchip.com/downloads/en/devicedoc/spi.pdf