请问一下我要如何正确的接收由PLC回传的RTU码
要如何用CKC去判 ..

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你说的是 Modbus RTU 的 CRC16 吧!?
每个 Packet 的最后两个 Byte 就是 CRC16

/* Table of CRC values for high-order byte */
unsigned char auchCRCHi[] = {
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,
0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,
0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40,
0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,
0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40,
0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40,
0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,
0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 } ;

/* Table of CRC values for low-order byte */
unsigned char auchCRCLo[] = {
0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06,
0x07, 0xC7, 0x05, 0xC5, 0xC4, 0x04, 0xCC, 0x0C, 0x0D, 0xCD,
0x0F, 0xCF, 0xCE, 0x0E, 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09,
0x08, 0xC8, 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A,
0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC, 0x14, 0xD4,
0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6, 0xD2, 0x12, 0x13, 0xD3,
0x11, 0xD1, 0xD0, 0x10, 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3,
0xF2, 0x32, 0x36, 0xF6, 0xF7, 0x37, 0xF5, 0x35, 0x34, 0xF4,
0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE, 0xFA, 0x3A,
0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38, 0x28, 0xE8, 0xE9, 0x29,
0xEB, 0x2B, 0x2A, 0xEA, 0xEE, 0x2E, 0x2F, 0xEF, 0x2D, 0xED,
0xEC, 0x2C, 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26,
0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0, 0xA0, 0x60,
0x61, 0xA1, 0x63, 0xA3, 0xA2, 0x62, 0x66, 0xA6, 0xA7, 0x67,
0xA5, 0x65, 0x64, 0xA4, 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F,
0x6E, 0xAE, 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68,
0x78, 0xB8, 0xB9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA, 0xBE, 0x7E,
0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C, 0xB4, 0x74, 0x75, 0xB5,
0x77, 0xB7, 0xB6, 0x76, 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71,
0x70, 0xB0, 0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92,
0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54, 0x9C, 0x5C,
0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E, 0x5A, 0x9A, 0x9B, 0x5B,
0x99, 0x59, 0x58, 0x98, 0x88, 0x48, 0x49, 0x89, 0x4B, 0x8B,
0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C,
0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42,
0x43, 0x83, 0x41, 0x81, 0x80, 0x40} ;

/* The function return the CRC as a type unsigned short. */
/* CRC Generation Function */
WORD CRC16(BYTE *puchMsg, int usDataLen)
{
  BYTE uchCRCHi = 0xFF;     /* high CRC byte initialized */
  BYTE uchCRCLo = 0xFF;     /* low CRC byte initialized */
  WORD uIndex;           /* will index index into lookup */

  while (usDataLen--)             /* pass through message buffer */
  {
    uIndex = uchCRCHi ^ *puchMsg++;
    uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex];
    uchCRCLo = auchCRCLo[uIndex];
  }
  return (uchCRCHi << 8 | uchCRCLo);
}

谢谢大大每次都不厌其烦的帮小弟

CRC:   MOV DPH, #table ; 指向余式表下半区
      MOV DPL, R0 ; 指向对应单元
      CLR A ;
      MOVC A, @A+DPTR ; 读余式的高位元组
      XRL A, R1 ; 计算余式的高位元组
      MOV R0, A ; 存入R0
      INC DPH ; 指向余式表上半区
      CLR A ;
      MOVC A, @A+DPTR ; 读余式的低位元组
      XRL A, R2 ; 计算余式的低位元组
      MOV R1, A ; 存入R1
      RET
table: 要如何写
谢谢

table 就是上面两个表接在一起, 只是它要求将 auchCRCHi, auchCRCLo 放在 256 bytes 的边界上
这个 CRC 副程式的参数好像是 R0(uchCRCHi), R1(uchCRCLo)
这样新的资料要加入CRC时不是要先计算 R0 跟新资料的 XOR?

我比较喜欢用下面的程式:

; /* Table of CRC values for high-order byte */
auchCRCHi     equ   $
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h
          db     00h, C1h, 81h, 40h, 00h, C1h, 81h, 40h, 01h, C0h
          db     80h, 41h, 01h, C0h, 80h, 41h, 00h, C1h, 81h, 40h
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 00h, C1h
          db     81h, 40h, 01h, C0h, 80h, 41h, 01h, C0h, 80h, 41h
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 00h, C1h
          db     81h, 40h, 00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h, 00h, C1h, 81h, 40h
          db     01h, C0h, 80h, 41h, 01h, C0h, 80h, 41h, 00h, C1h
          db     81h, 40h, 01h, C0h, 80h, 41h, 00h, C1h, 81h, 40h
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h, 00h, C1h, 81h, 40h
          db     01h, C0h, 80h, 41h, 00h, C1h, 81h, 40h, 01h, C0h
          db     80h, 41h, 01h, C0h, 80h, 41h, 00h, C1h, 81h, 40h
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h
          db     00h, C1h, 81h, 40h, 00h, C1h, 81h, 40h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h
          db     01h, C0h, 80h, 41h, 00h, C1h, 81h, 40h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h, 00h, C1h, 81h, 40h
          db     01h, C0h, 80h, 41h, 01h, C0h, 80h, 41h, 00h, C1h
          db     81h, 40h, 00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h
          db     00h, C1h, 81h, 40h, 01h, C0h, 80h, 41h, 01h, C0h
          db     80h, 41h, 00h, C1h, 81h, 40h

; /* Table of CRC values for low-order byte */
auchCRCLo     equ   $
          db     00h, C0h, C1h, 01h, C3h, 03h, 02h, C2h, C6h, 06h
          db     07h, C7h, 05h, C5h, C4h, 04h, CCh, 0Ch, 0Dh, CDh
          db     0Fh, CFh, CEh, 0Eh, 0Ah, CAh, CBh, 0Bh, C9h, 09h
          db     08h, C8h, D8h, 18h, 19h, D9h, 1Bh, DBh, DAh, 1Ah
          db     1Eh, DEh, DFh, 1Fh, DDh, 1Dh, 1Ch, DCh, 14h, D4h
          db     D5h, 15h, D7h, 17h, 16h, D6h, D2h, 12h, 13h, D3h
          db     11h, D1h, D0h, 10h, F0h, 30h, 31h, F1h, 33h, F3h
          db     F2h, 32h, 36h, F6h, F7h, 37h, F5h, 35h, 34h, F4h
          db     3Ch, FCh, FDh, 3Dh, FFh, 3Fh, 3Eh, FEh, FAh, 3Ah
          db     3Bh, FBh, 39h, F9h, F8h, 38h, 28h, E8h, E9h, 29h
          db     EBh, 2Bh, 2Ah, EAh, EEh, 2Eh, 2Fh, EFh, 2Dh, EDh
          db     ECh, 2Ch, E4h, 24h, 25h, E5h, 27h, E7h, E6h, 26h
          db     22h, E2h, E3h, 23h, E1h, 21h, 20h, E0h, A0h, 60h
          db     61h, A1h, 63h, A3h, A2h, 62h, 66h, A6h, A7h, 67h
          db     A5h, 65h, 64h, A4h, 6Ch, ACh, ADh, 6Dh, AFh, 6Fh
          db     6Eh, AEh, AAh, 6Ah, 6Bh, ABh, 69h, A9h, A8h, 68h
          db     78h, B8h, B9h, 79h, BBh, 7Bh, 7Ah, BAh, BEh, 7Eh
          db     7Fh, BFh, 7Dh, BDh, BCh, 7Ch, B4h, 74h, 75h, B5h
          db     77h, B7h, B6h, 76h, 72h, B2h, B3h, 73h, B1h, 71h
          db     70h, B0h, 50h, 90h, 91h, 51h, 93h, 53h, 52h, 92h
          db     96h, 56h, 57h, 97h, 55h, 95h, 94h, 54h, 9Ch, 5Ch
          db     5Dh, 9Dh, 5Fh, 9Fh, 9Eh, 5Eh, 5Ah, 9Ah, 9Bh, 5Bh
          db     99h, 59h, 58h, 98h, 88h, 48h, 49h, 89h, 4Bh, 8Bh
          db     8Ah, 4Ah, 4Eh, 8Eh, 8Fh, 4Fh, 8Dh, 4Dh, 4Ch, 8Ch
          db     44h, 84h, 85h, 45h, 87h, 47h, 46h, 86h, 82h, 42h
          db     43h, 83h, 41h, 81h, 80h, 40h

CRC16:
    xrl   a, uchCRCHi   ; uIndex = uchCRCHi ^ *puchMsg++;
    mov   r7, a
    mov   dptr, #auchCRCHi
    movc   a, @a+dptr
    xrl   a, uchCRCLo
    mov   uchCRCHi, a   ; uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex];
    mov   dptr, #auchCRCLo
    mov   a, r7
    movc   a, @a+dptr
    mov   uchCRCLo, a   ; uchCRCLo = auchCRCLo[uIndex];
    ret

SendReadHolding:
    mov   uchCRCHi, #0FFh
    mov   uchCRCLo, #0FFh
    ;
    mov   a, #01h       ; Address
    call   SendChar
    call   CRC16
    mov   a, #03h       ; Function Code = 03 (Read Holding Registers)
    call   SendChar
    call   CRC16
    ;
    mov   a, #00h
    call   SendChar
    call   CRC16
    mov   a, #00h       ; Register Address 0000h
    call   SendChar
    call   CRC16
    ;
    mov   a, #00h
    call   SendChar
    call   CRC16
    mov   a, #01h       ; Regisetr Count 0001h
    call   SendChar
    call   CRC16
    ;
    mov   a, uchCRCHi
    call   SendChar
    mov   a, uchCRCLo
    call   SendChar
    ret

谢谢大大的帮助
可不可以再请教一下
要如何用TB8, RB8做奇同位或偶同位检查
还有要如何把资料先收到的一直往高位址推
就是如果我连续收到30 31 32时就把30丢到72H里
                                31     71H'
                                32     70H

如果是连续收到30 31 32 33时就把30 丢到73H
                                31     72H
                                32     71H
                                33     70H
就是把最后收到的位元组放在最低的位址
谢谢

51 本身就有偶同位的 P 位元可以使用(P 位元为 ACC 的偶同位)
因此你只要先将 SCON 设成 9-bit UART (SCON=D0h)
然后传送部分:
; 偶同位
    mov   a, #01h
    mov   c, p
    mov   tb8, c
    call   SendChar
; 奇同位
    mov   a, #01h
    mov   c, p
    cpl   c
    mov   tb8, c
    call   SendChar

为何要把最后收到的资料放在最低位址?
一般要做这个必须要知道有多大的空间可以放及目前要放几个
然后使用 xch 指令来做, 例如用简单的范例来说(假设ACC为收到的资料)
; 范例一: 确定只有三个Bytes空间
    xch   a, 70h
    xch   a, 71h
    xch   a, 72h
; 范例二: 使用 R0, R2 来指定位址及空间大小
    mov   r0, #70h
    mov   r2, #3
Serial_Shift:
    xch   a, @r0
    inc   r0
    djnz   r2, Serial_Shift

不好意思在请问一下大大教小弟的115200bps
mov T2CON, #00110000b
mov RCAP2H, #HIGH (-3) ; -3 = 65533
mov RCAP2L, #LOW (-3)
mov TH2, RCAP2H
mov TL2, RCAP2L
setb TR2

设鲍率为115200bps
我用11.0592的石英震荡晶体
我用两颗8051做传输没有问题
但是我用南桦电机的rs232监听软体
和我的8051做rs232的传输
有收到东西却是乱码
谢谢

看起来没问题! 你有检查南华电机所使用的格式跟你一样?
例如 8 Data bits, None parity, 1 Stop bit 还是其他格式?

ORG   00h      
      mov T2CON, #00110000b
      mov RCAP2H, #(-3) ; -3 = 65533
      mov RCAP2L, #(-3)
      mov TH2, RCAP2H
      mov TL2, RCAP2L
      setb   TR2
      mov   scon,#01110000b

我以经试过了格式是一样的

mov   scon,#01110000b <- 你的格式是 8 Data bits, None Parity, 1 Stop bit

一般出现这种问题都是找第三个设备来测试. 例如电脑就是很好的监测设备
只要电脑用相同的格式接到正确的资料那就没问题了. 再来的问题应该就是板子或程式的问题了.