16位绝对编码器SSI接口

大家好！我使用PIC18f4550/PIC18f4431作为通过SSI/SPI协议的绝对编码器接口，分别借助于差分线驱动器/接收器IC(AM26LS31x和AM26LS32Ax)。编码器模型；BEI M40系列，绝对，64圈，灰色编码，串行RS422协议。现在的问题是：当位置改变（编码器旋转）时，串行移位寄存器输出到MCU端的缓冲寄存器（SSPBUF）的随机值跳到附近。但是，当编码器是静止的（没有旋转）、位置值ok和一致的.xc8代码SPI读取功能块：无符号字符._ReadSPI（void）{无符号字符TemVar1、TemVar2、TemVar3；无符号字符第一字节[3]、编码器[3]；LATAbits.LA5=0；//enable read slavePIR1bits.SSPIF=。0；//清除中断标志//SSPSTATBITS.BF＝0；SSPBUF＝0x00；/ /启动总线循环；（！）PIR1bits.SSPIF)；//等待直到周期完成//Delay1KTCYx(10)；TemVar1=SSPBUF；PIR1bits.SSPIF=0；SSPBUF=0x00；//启动总线周期(!PIR1bits.SSPIF)；//等待直到周期完成//Delay1KTCYx(10)；TemVar2=SSPBUF；//Delay1KTCYx(10)；PIR1bits.SSPIF=0；SSPBUF=0x00；//启动总线周期(!PIR1bits.SSPIF)；//等待直到循环完成//Delay1KTCYx(10)；TemVar3=SSPBUF；//Delay1KTCYx(10)；LATAbits.LATA5=1；//enable read slave//在数据循环读取.my_putsUSART(“ABSOLUTE ENCODER=”)、sprintf(firstbyte,“%u”,TemVar2)；//type转换//my_putsUSART(“2stByteTest=”)；putsUSART（第一字节）；//1sy字节到PCmy_putsUSART（“”）；sprintf（编码器，“%u”，TemVar3）；//type转换为无符号chARMy_putsUSART（编码器）；//2字节到PC.（0）；//return with byte read}朋友请提供一些输入来修复它。非常感谢您的期待。



      以下为原文

    Hi everybody!
I am using PIC18f4550/PIC18f4431 for absolute encoder interface through SSI/SPI protocol with the help of differential line driver/receiver ICs  respectively (AM26LS31x andAM26LS32Ax). Encoder model; BEI M40 series, absolute, 64 turn,grey coded, serial RS422 protocol.
Now the problem is: The serial shift register output  into buffer register at MCU end (SSPBUF) jumps to near by random value when position changes (encoder rotates). but there is  no any jumps when encoder is stationary (no rotation), position value ok and consistent.
xc8 code SPI read function block:
unsigned char My_ReadSPI( void )
{
unsigned char TemVar1, TemVar2, TemVar3;
unsigned char firstbyte[3], encoder[3];

LATAbits.LA5 = 0; //enable read slave
PIR1bits.SSPIF = 0; // Clear interrupt flag
//SSPSTATbits.BF = 0;
SSPBUF = 0x00; // initiate bus cycle
while(!PIR1bits.SSPIF); // wait until cycle complete
// Delay1KTCYx(10);
TemVar1 = SSPBUF;

PIR1bits.SSPIF = 0;
SSPBUF = 0x00; //initiate bus cycle
while(!PIR1bits.SSPIF); // wait until cycle complete
//Delay1KTCYx(10);
TemVar2 = SSPBUF;
//Delay1KTCYx(10);

PIR1bits.SSPIF = 0;
SSPBUF = 0x00; //initiate bus cycle
while(!PIR1bits.SSPIF); // wait until cycle complete
//Delay1KTCYx(10);
TemVar3 = SSPBUF;
//Delay1KTCYx(10);
LATAbits.LATA5 = 1; //enable read slave //after the data cycle read disable


my_putsUSART("ABSOLUTE ENCODER = ");
sprintf(firstbyte, "%u", TemVar2); //type conversion
//my_putsUSART("2st Byte Test = ");
my_putsUSART(firstbyte);           //1sy byte to PC
my_putsUSART(" ");
sprintf(encoder, "%u", TemVar3); //type conversion to unsigned char
my_putsUSART(encoder);             //2nd byte to PC

return (0); // return with byte read

}
Friends please give some inputs to fix it.
thank you very much in anticipation.
Sjorphail