关于SPI双机互为主从的通信

onbluesun

SPI单主单从试了很多次，数据总是乱飞，现在决定用互为主从通信，依然碰到错误，错误如下。
每次开机后，主机发送数据给从机，从机返回这个数据到主机，但是主机收到的数据是0x00，开机后第一次通信总是这样，之后就正常了，第二次给从机发送数据就能返回正常的数据了。根据测试，从机收到的数据是正常的，但是将数据返回给主机，数据就不正常了，程序如下：

1. #include "reg51.h"
   
2. #define FOSC 22118400L
   
3. #define BAUD (256 - FOSC / 32 / 115200)
   
4. typedef unsigned char BYTE;
   
5. typedef unsigned int WORD;
   
6. typedef unsigned long DWORD;
   
7. sfr AUXR = 0x8e; //Auxiliary register
   
8. sfr SPSTAT = 0xcd; //SPI status register
   
9. #define SPIF 0x80 //SPSTAT.7
   
10. #define WCOL 0x40 //SPSTAT.6
    
11. sfr SPCTL = 0xce; //SPI control register
    
12. #define SSIG 0x80 //SPCTL.7
    
13. #define SPEN 0x40 //SPCTL.6
    
14. #define DORD 0x20 //SPCTL.5
    
15. #define MSTR 0x10 //SPCTL.4
    
16. #define CPOL 0x08 //SPCTL.3
    
17. #define CPHA 0x04 //SPCTL.2
    
18. #define SPDHH 0x00 //CPU_CLK/4
    
19. #define SPDH 0x01 //CPU_CLK/16
    
20. #define SPDL 0x02 //CPU_CLK/64
    
21. #define SPDLL 0x03 //CPU_CLK/128
    
22. sfr SPDAT = 0xcf; //SPI data register
    
23. sbit SPISS = P1^3; //SPI slave select, connect to other MCU's SS(P1.4) pin
    
24. sfr IE2 = 0xAF; //interrupt enable rgister 2
    
25. #define ESPI 0x02 //IE2.1
    
26. void InitUart();
    
27. void InitSPI();
    
28. void SendUart(BYTE dat); //send data to PC
    
29. BYTE RecvUart(); //receive data from PC
    
30. bit MSSEL; //1: master 0:slave
    
31. ///////////////////////////////////////////////////////////
    
32. void main()
    
33. {
    
34. InitUart(); //initial UART
    
35. InitSPI(); //initial SPI
    
36. IE2 |= ESPI;
    
37. EA = 1;
    
38. while (1)
    
39. {
    
40. if (RI)
    
41. {
    
42. SPCTL = SPEN | MSTR; //set as master
    
43. MSSEL = 1;
    
44. ACC = RecvUart();
    
45. SPISS = 0; //pull low slave SS
    
46. SPDAT = ACC; //trigger SPI send
    
47. }
    
48. }
    
49. }
    
50. ///////////////////////////////////////////////////////////
    
51. void spi_isr() interrupt 9 using 1 //SPI interrupt routine 9 (004BH)
    
52. {
    
53. SPSTAT = SPIF | WCOL; //clear SPI status
    
54. if (MSSEL)
    
55. {
    
56. SPCTL = SPEN; //reset as slave
    
57. MSSEL = 0;
    
58. SPISS = 1; //push high slave SS
    
59. SendUart(SPDAT); //return received SPI data
    
60. }
    
61. else
    
62. { //for salve (receive SPI data from master and
    
63. SPDAT = SPDAT; // send previous SPI data to master)
    
64. }
    
65. }
    
66. ///////////////////////////////////////////////////////////
    
67. void InitUart()
    
68. {
    
69. SCON = 0x5a; //set UART mode as 8-bit variable baudrate
    
70. TMOD = 0x20; //timer1 as 8-bit auto reload mode
    
71. AUXR = 0x40; //timer1 work at 1T mode
    
72. TH1 = TL1 = BAUD; //11 5200 bps
    
73. TR1 = 1;
    
74. }
    
75. ///////////////////////////////////////////////////////////
    
76. void InitSPI()
    
77. {
    
78. SPDAT = 0; //initial SPI data
    
79. SPSTAT = SPIF | WCOL; //clear SPI status
    
80. SPCTL = SPEN; //slave mode
    
81. }
    
82. ///////////////////////////////////////////////////////////
    
83. void SendUart(BYTE dat)
    
84. {
    
85. while (!TI); //wait pre-data sent
    
86. TI = 0; //clear TI flag
    
87. SBUF = dat; //send current data
    
88. }
    
89. ///////////////////////////////////////////////////////////
    
90. BYTE RecvUart()
    
91. {
    
92. while (!RI); //wait receive complete
    
93. RI = 0; //clear RI flag
    
94. return SBUF; //return receive data
    
95. }

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onbluesun

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