Cómo obtener datos de 10 bits de ADC usando el protocolo SPI

Estoy haciendo una implementación de esclavo múltiple maestro único.
Maestro - PIC18F4550
Esclavo - PIC18F4520

Un potenciómetro está conectado al Esclavo. El esclavo convertirá el valor del potenciómetro a digital y se comunicará con el maestro mediante el protocolo SPI.

Recibo datos de 8 bits (ADRESH - Justificado a la izquierda) correctamente del esclavo. Pero tengo que obtener datos de 10 bits (ADRESH - 8 bits, ADRESL - 2 bits).

¿Cómo puedo obtener datos de 10 bits?

Codigo maestro

OpenSPI(SPI_FOSC_64, MODE_01, SMPMID);   //SPI configuration

SSPCON1bits.WCOL = 0;    //Clearing SSPBUF
LATDbits.LATD0 = 0;  //Slave select
WriteSPI(0xFF);  //writing 0xFF to slave    
for(mdelay = 0; mdelay < 10; mdelay++); 
var1 = SSPBUF;
LATDbits.LATD0 = 1;
highbyte = var1;
highbyte = highbyte << 8;    //deselecting SS   
for(mdelay = 0; mdelay < 100; mdelay++);

SSPCON1bits.WCOL = 0;
LATDbits.LATD0 = 0;  //2nd time slave selct 
WriteSPI(0xAA);
for(mdelay = 0; mdelay < 10; mdelay++); 
var2 = SSPBUF;
LATDbits.LATD0 = 1;
lowbyte = var2;
for(mdelay = 0; mdelay < 100; mdelay++);

highbyte = highbyte | lowbyte;
result = highbyte;

Esclavo

int Count;
unsigned char ch1,ch2,data; 

ADCON0 = 0x01;   // AD Control Register 1: Enable (turn on ADC)
ADCON2 = 0x3C;   // AD Control Register 2: 20 TAD (accuracy), FOSC 4 (freq/4)
ADCON2bits.ADFM = 0;     // ADC result left justified (D10 - D2 --> ADRESH, D1 - D0 --> ADRESL) 

TRISCbits.TRISC3 = 1;    //SPI pins(PIC18F4520)
TRISCbits.TRISC4 = 1;   
TRISCbits.TRISC5 = 0;
TRISAbits.TRISA5 = 1;

TRISDbits.TRISD0 = 0;    //Configuring PORTD as output
TRISDbits.TRISD1 = 0;
TRISDbits.TRISD2 = 0;
TRISDbits.TRISD3 = 0;
TRISDbits.TRISD4 = 0;
TRISDbits.TRISD5 = 0;
TRISDbits.TRISD6 = 0;
TRISDbits.TRISD7 = 0;   

SSPSTATbits.SMP = 0;     //Configuration of SPI register
SSPSTATbits.CKE = 0;
SSPCON1bits.CKP = 0;
SSPCON1bits.SSPM3 = 0;
SSPCON1bits.SSPM2 = 1;
SSPCON1bits.SSPM1 = 0;
SSPCON1bits.SSPM0 = 0;  
SSPCON1bits.SSPEN = 1;

while(1)
{   

ADCON0bits.CHS0 = 1;     //Selecting AN0 as analog input
ADCON0bits.CHS1 = 0;
ADCON0bits.CHS2 = 0;
ADCON0bits.CHS3 = 0;
ADCON0bits.GO = 1;   //Start analog to digital conversion   
while (ADCON0bits.NOT_DONE);    
ch1 = ADRESL;   
ch2 = ADRESH;


data = SSPBUF;   //loading the SSPBUF value to some dummy varible(Previous data in SSPBUF)

//First time slave select
SSPCON1bits.WCOL = 0;    //Clearing SSPBUF register
while(PORTAbits.RA5 == 1);  //wait for slave select
SSPBUF = ch1;    //Loading ADRESH value to SSPBUF
while(SSPSTATbits.BF == 0); //wait untill the buffer is full

for(Count=0;Count<10;Count++);  //delay

//Second time slave selct
SSPCON1bits.WCOL = 0;    //Clearing SSPBUF register
while(PORTAbits.RA5 == 1);  //wait for slave select
SSPBUF = ch2;    //Loading ADRESL value to SSPBUF
while(SSPSTATbits.BF == 0); //wait untill the buffer is full

for(Count=0;Count<10;Count++);  //delay
}