找个会CRC-16（CCITT）的人，有没有？？？(200分)

我现在想澄清一个问题：
效验码的意义——到底是(1)需要效验的字符串，如果加上效验码以后，通过某个多项式进行
效验，如果最后结果为0，说明效验成功；(2)通过某个多项式对需要进行效验的字符串进行
效验，如果产生的效验码和发送者计算得到并附加在字符串后面的效验码相同，则对接收到
的内容视为正确。
————————————————
大家说说，到底(1)对？还是(2)对？？？

（1）是原始定义，其实（2）也对。都一样！

我的邮箱catbrother@163.net

catbrother说的对，两者实际上是一样的，我觉得还是算法的问题，你用的是仪器，
不能找厂家问一下通讯协议？

厂家已经提供开放协议了，就是我在第一个帖子说的内容，其他的就不好说了，因为厂家是澳大利亚的。

串口工具
我要！！！！！！

to catbrother
这么急，我已经给我发了。：P

[?][?][?][?]

{*************************************************************}
{ CRC Calculator Unit for Delphi 16/32 }
{ Version: 2.0 }
{ Author: Aleksey Kuznetsov }
{ E-Mail: aleksey@utilmind.com }
{ Home Page: http://www.utilmind.com }
{ Created: March, 30, 1999 for Karol Suchanek }
{ Modified: April, 6, 1999 }
{ Legal: Copyright (c) 1999, UtilMind Solutions }
{ Idea: Edwin T. Floyd }
{*************************************************************}
{ This unit provides three speed-optimized functions to }
{ compute (or continue computation of) a Cyclic Redundency }
{ Check (CRC). Applicable to XModem protocol (16-bit CRC), }
{ SEA's "ARC" utility, PKZip (32-bit CRC) and many others }
{ compatible software. }
{ Please see TESTCRC.DPR for example. }
{*************************************************************}
{ Each function takes three parameters: }
{ }
{ InitCRC - The initial CRC value. This may be the }
{ recommended initialization value if this is the first or }
{ only block to be checked, or this may be a previously }
{ computed CRC value if this is a continuation. }
{ XModem and ARC usually starts with zero (0), 32 bit crc }
{ starts with all bits on ($FFFFFFFF). }
{ }
{ Buffer - An untyped parameter (Pointer^) specifying the }
{ beginning of the memory area to be checked. }
{ }
{ Length - A word indicating the length of the memory area to }
{ be checked. If Length is zero, the function returns the }
{ value of InitCRC. }
{ }
{ The function result is the updated CRC. }
{*************************************************************}

unit CRC;

interface

function UpdateCRC16(InitCRC: Word; var Buffer;
Length: {$IFDEF Win32} LongInt {$ELSE} Word {$ENDIF}): Word;
{ I believe this is the CRC used by the XModem protocol.
The transmitting end should initialize with zero, UpdateCRC16 for
the block, Continue the UpdateCRC16 for two nulls, and append the
result (hi order byte first) to the transmitted block. The receiver
should initialize with zero and UpdateCRC16 for the received block
including the two byte CRC. The result will be zero (why?) if there
were no transmission errors. (I have not tested this function with
an actual XModem implementation, though I did verify the behavior
just described. See TESTCRC.DPR.) }

function UpdateCRCArc(InitCRC: Word; var Buffer;
Length: {$IFDEF Win32} LongInt {$ELSE} Word {$ENDIF}): Word;
{ This function computes the CRC used by SEA's ARC utility.
Initialize with zero.}

function UpdateCRC32(InitCRC: LongInt; var Buffer;
{$IFDEF Win32} Length: LongInt {$ELSE} Length: Word {$ENDIF}): LongInt;
{ This function computes the CRC used by PKZIP and Forsberg's ZModem.
Initialize with high-values ($FFFFFFFF), and finish by inverting
allbits (Not). }

function FileCRC16(FileName: String; var CRC16: Word): Boolean; { Return True if ok }
function FileCRCArc(FileName: String; var CRCArc: Word): Boolean; { Return True if ok }
function FileCRC32(FileName: String; var CRC32: LongInt): Boolean; { Return True if ok }

implementation

const
CrcArcTab: Array[0..$FF] of Word =
($00000, $0C0C1, $0C181, $00140, $0C301, $003C0, $00280, $0C241,
$0C601, $006C0, $00780, $0C741, $00500, $0C5C1, $0C481, $00440,
$0CC01, $00CC0, $00D80, $0CD41, $00F00, $0CFC1, $0CE81, $00E40,
$00A00, $0CAC1, $0CB81, $00B40, $0C901, $009C0, $00880, $0C841,
$0D801, $018C0, $01980, $0D941, $01B00, $0DBC1, $0DA81, $01A40,
$01E00, $0DEC1, $0DF81, $01F40, $0DD01, $01DC0, $01C80, $0DC41,
$01400, $0D4C1, $0D581, $01540, $0D701, $017C0, $01680, $0D641,
$0D201, $012C0, $01380, $0D341, $01100, $0D1C1, $0D081, $01040,
$0F001, $030C0, $03180, $0F141, $03300, $0F3C1, $0F281, $03240,
$03600, $0F6C1, $0F781, $03740, $0F501, $035C0, $03480, $0F441,
$03C00, $0FCC1, $0FD81, $03D40, $0FF01, $03FC0, $03E80, $0FE41,
$0FA01, $03AC0, $03B80, $0FB41, $03900, $0F9C1, $0F881, $03840,
$02800, $0E8C1, $0E981, $02940, $0EB01, $02BC0, $02A80, $0EA41,
$0EE01, $02EC0, $02F80, $0EF41, $02D00, $0EDC1, $0EC81, $02C40,
$0E401, $024C0, $02580, $0E541, $02700, $0E7C1, $0E681, $02640,
$02200, $0E2C1, $0E381, $02340, $0E101, $021C0, $02080, $0E041,
$0A001, $060C0, $06180, $0A141, $06300, $0A3C1, $0A281, $06240,
$06600, $0A6C1, $0A781, $06740, $0A501, $065C0, $06480, $0A441,
$06C00, $0ACC1, $0AD81, $06D40, $0AF01, $06FC0, $06E80, $0AE41,
$0AA01, $06AC0, $06B80, $0AB41, $06900, $0A9C1, $0A881, $06840,
$07800, $0B8C1, $0B981, $07940, $0BB01, $07BC0, $07A80, $0BA41,
$0BE01, $07EC0, $07F80, $0BF41, $07D00, $0BDC1, $0BC81, $07C40,
$0B401, $074C0, $07580, $0B541, $07700, $0B7C1, $0B681, $07640,
$07200, $0B2C1, $0B381, $07340, $0B101, $071C0, $07080, $0B041,
$05000, $090C1, $09181, $05140, $09301, $053C0, $05280, $09241,
$09601, $056C0, $05780, $09741, $05500, $095C1, $09481, $05440,
$09C01, $05CC0, $05D80, $09D41, $05F00, $09FC1, $09E81, $05E40,
$05A00, $09AC1, $09B81, $05B40, $09901, $059C0, $05880, $09841,
$08801, $048C0, $04980, $08941, $04B00, $08BC1, $08A81, $04A40,
$04E00, $08EC1, $08F81, $04F40, $08D01, $04DC0, $04C80, $08C41,
$04400, $084C1, $08581, $04540, $08701, $047C0, $04680, $08641,
$08201, $042C0, $04380, $08341, $04100, $081C1, $08081, $04040);

Crc16Tab: Array[0..$FF] of Word =
($00000, $01021, $02042, $03063, $04084, $050a5, $060c6, $070e7,
$08108, $09129, $0a14a, $0b16b, $0c18c, $0d1ad, $0e1ce, $0f1ef,
$01231, $00210, $03273, $02252, $052b5, $04294, $072f7, $062d6,
$09339, $08318, $0b37b, $0a35a, $0d3bd, $0c39c, $0f3ff, $0e3de,
$02462, $03443, $00420, $01401, $064e6, $074c7, $044a4, $05485,
$0a56a, $0b54b, $08528, $09509, $0e5ee, $0f5cf, $0c5ac, $0d58d,
$03653, $02672, $01611, $00630, $076d7, $066f6, $05695, $046b4,
$0b75b, $0a77a, $09719, $08738, $0f7df, $0e7fe, $0d79d, $0c7bc,
$048c4, $058e5, $06886, $078a7, $00840, $01861, $02802, $03823,
$0c9cc, $0d9ed, $0e98e, $0f9af, $08948, $09969, $0a90a, $0b92b,
$05af5, $04ad4, $07ab7, $06a96, $01a71, $00a50, $03a33, $02a12,
$0dbfd, $0cbdc, $0fbbf, $0eb9e, $09b79, $08b58, $0bb3b, $0ab1a,
$06ca6, $07c87, $04ce4, $05cc5, $02c22, $03c03, $00c60, $01c41,
$0edae, $0fd8f, $0cdec, $0ddcd, $0ad2a, $0bd0b, $08d68, $09d49,
$07e97, $06eb6, $05ed5, $04ef4, $03e13, $02e32, $01e51, $00e70,
$0ff9f, $0efbe, $0dfdd, $0cffc, $0bf1b, $0af3a, $09f59, $08f78,
$09188, $081a9, $0b1ca, $0a1eb, $0d10c, $0c12d, $0f14e, $0e16f,
$01080, $000a1, $030c2, $020e3, $05004, $04025, $07046, $06067,
$083b9, $09398, $0a3fb, $0b3da, $0c33d, $0d31c, $0e37f, $0f35e,
$002b1, $01290, $022f3, $032d2, $04235, $05214, $06277, $07256,
$0b5ea, $0a5cb, $095a8, $08589, $0f56e, $0e54f, $0d52c, $0c50d,
$034e2, $024c3, $014a0, $00481, $07466, $06447, $05424, $04405,
$0a7db, $0b7fa, $08799, $097b8, $0e75f, $0f77e, $0c71d, $0d73c,
$026d3, $036f2, $00691, $016b0, $06657, $07676, $04615, $05634,
$0d94c, $0c96d, $0f90e, $0e92f, $099c8, $089e9, $0b98a, $0a9ab,
$05844, $04865, $07806, $06827, $018c0, $008e1, $03882, $028a3,
$0cb7d, $0db5c, $0eb3f, $0fb1e, $08bf9, $09bd8, $0abbb, $0bb9a,
$04a75, $05a54, $06a37, $07a16, $00af1, $01ad0, $02ab3, $03a92,
$0fd2e, $0ed0f, $0dd6c, $0cd4d, $0bdaa, $0ad8b, $09de8, $08dc9,
$07c26, $06c07, $05c64, $04c45, $03ca2, $02c83, $01ce0, $00cc1,
$0ef1f, $0ff3e, $0cf5d, $0df7c, $0af9b, $0bfba, $08fd9, $09ff8,
$06e17, $07e36, $04e55, $05e74, $02e93, $03eb2, $00ed1, $01ef0);

Crc32Tab: Array[0..$FF] of LongInt =
($00000000, $77073096, $ee0e612c, $990951ba, $076dc419, $706af48f,
$e963a535, $9e6495a3, $0edb8832, $79dcb8a4, $e0d5e91e, $97d2d988,
$09b64c2b, $7eb17cbd, $e7b82d07, $90bf1d91, $1db71064, $6ab020f2,
$f3b97148, $84be41de, $1adad47d, $6ddde4eb, $f4d4b551, $83d385c7,
$136c9856, $646ba8c0, $fd62f97a, $8a65c9ec, $14015c4f, $63066cd9,
$fa0f3d63, $8d080df5, $3b6e20c8, $4c69105e, $d56041e4, $a2677172,
$3c03e4d1, $4b04d447, $d20d85fd, $a50ab56b, $35b5a8fa, $42b2986c,
$dbbbc9d6, $acbcf940, $32d86ce3, $45df5c75, $dcd60dcf, $abd13d59,
$26d930ac, $51de003a, $c8d75180, $bfd06116, $21b4f4b5, $56b3c423,
$cfba9599, $b8bda50f, $2802b89e, $5f058808, $c60cd9b2, $b10be924,
$2f6f7c87, $58684c11, $c1611dab, $b6662d3d, $76dc4190, $01db7106,
$98d220bc, $efd5102a, $71b18589, $06b6b51f, $9fbfe4a5, $e8b8d433,
$7807c9a2, $0f00f934, $9609a88e, $e10e9818, $7f6a0dbb, $086d3d2d,
$91646c97, $e6635c01, $6b6b51f4, $1c6c6162, $856530d8, $f262004e,
$6c0695ed, $1b01a57b, $8208f4c1, $f50fc457, $65b0d9c6, $12b7e950,
$8bbeb8ea, $fcb9887c, $62dd1ddf, $15da2d49, $8cd37cf3, $fbd44c65,
$4db26158, $3ab551ce, $a3bc0074, $d4bb30e2, $4adfa541, $3dd895d7,
$a4d1c46d, $d3d6f4fb, $4369e96a, $346ed9fc, $ad678846, $da60b8d0,
$44042d73, $33031de5, $aa0a4c5f, $dd0d7cc9, $5005713c, $270241aa,
$be0b1010, $c90c2086, $5768b525, $206f85b3, $b966d409, $ce61e49f,
$5edef90e, $29d9c998, $b0d09822, $c7d7a8b4, $59b33d17, $2eb40d81,
$b7bd5c3b, $c0ba6cad, $edb88320, $9abfb3b6, $03b6e20c, $74b1d29a,
$ead54739, $9dd277af, $04db2615, $73dc1683, $e3630b12, $94643b84,
$0d6d6a3e, $7a6a5aa8, $e40ecf0b, $9309ff9d, $0a00ae27, $7d079eb1,
$f00f9344, $8708a3d2, $1e01f268, $6906c2fe, $f762575d, $806567cb,
$196c3671, $6e6b06e7, $fed41b76, $89d32be0, $10da7a5a, $67dd4acc,
$f9b9df6f, $8ebeeff9, $17b7be43, $60b08ed5, $d6d6a3e8, $a1d1937e,
$38d8c2c4, $4fdff252, $d1bb67f1, $a6bc5767, $3fb506dd, $48b2364b,
$d80d2bda, $af0a1b4c, $36034af6, $41047a60, $df60efc3, $a867df55,
$316e8eef, $4669be79, $cb61b38c, $bc66831a, $256fd2a0, $5268e236,
$cc0c7795, $bb0b4703, $220216b9, $5505262f, $c5ba3bbe, $b2bd0b28,
$2bb45a92, $5cb36a04, $c2d7ffa7, $b5d0cf31, $2cd99e8b, $5bdeae1d,
$9b64c2b0, $ec63f226, $756aa39c, $026d930a, $9c0906a9, $eb0e363f,
$72076785, $05005713, $95bf4a82, $e2b87a14, $7bb12bae, $0cb61b38,
$92d28e9b, $e5d5be0d, $7cdcefb7, $0bdbdf21, $86d3d2d4, $f1d4e242,
$68ddb3f8, $1fda836e, $81be16cd, $f6b9265b, $6fb077e1, $18b74777,
$88085ae6, $ff0f6a70, $66063bca, $11010b5c, $8f659eff, $f862ae69,
$616bffd3, $166ccf45, $a00ae278, $d70dd2ee, $4e048354, $3903b3c2,
$a7672661, $d06016f7, $4969474d, $3e6e77db, $aed16a4a, $d9d65adc,
$40df0b66, $37d83bf0, $a9bcae53, $debb9ec5, $47b2cf7f, $30b5ffe9,
$bdbdf21c, $cabac28a, $53b39330, $24b4a3a6, $bad03605, $cdd70693,
$54de5729, $23d967bf, $b3667a2e, $c4614ab8, $5d681b02, $2a6f2b94,
$b40bbe37, $c30c8ea1, $5a05df1b, $2d02ef8d);

function UpdateCRC16(InitCRC: Word; var Buffer;
Length: {$IFDEF Win32} LongInt {$ELSE} Word {$ENDIF}): Word;
begin
asm
{$IFDEF Win32}
push esi
push edi
push eax
push ebx
push ecx
push edx
lea edi, Crc16Tab
mov esi, Buffer
mov ax, InitCrc
mov ecx, Length
or ecx, ecx
jz @@done
@@loop:
xor ebx, ebx
mov bl, ah
mov ah, al
lodsb
shl bx, 1
add ebx, edi
xor ax, [ebx]
loop @@loop
@@done:
mov Result, ax
pop edx
pop ecx
pop ebx
pop eax
pop edi
pop esi
{$ELSE}
lea di, Crc16Tab
push ds
pop es
push ds
lds si, Buffer
mov ax, InitCrc
mov cx, Length
or cx, cx
jz @@done
@@loop:
xor bx, bx
mov bl, ah
mov ah, al
lodsb
shl bx, 1
xor ax, es:[di + bx]
loop @@loop
pop ds
@@done:
mov Result, ax
{$ENDIF}
end;
end;

function UpdateCRCArc(InitCRC: Word; var Buffer;
Length: {$IFDEF Win32} LongInt {$ELSE} Word {$ENDIF}): Word;
begin
asm
{$IFDEF Win32}
push esi
push edi
push eax
push ebx
push ecx
push edx
lea edi, CrcArcTab
mov esi, Buffer
mov ax, InitCrc
mov ecx, Length
or ecx, ecx
jz @@done
@@loop:
xor ebx, ebx
mov bl, al
lodsb
xor bl, al
shl bx, 1
add ebx, edi
mov bx, [ebx]
xor bl, ah
mov ax, bx
loop @@loop
@@done:
mov Result, ax
pop edx
pop ecx
pop ebx
pop eax
pop edi
pop esi
{$ELSE}
lea di, CrcArcTab
push ds
pop es
push ds
lds si, Buffer
mov ax, InitCrc
mov cx, Length
or cx, cx
jz @@done
@@loop:
xor bx, bx
mov bl, al
lodsb
xor bl, al
shl bx, 1
mov bx, es:[di + bx]
xor bl, ah
mov ax, bx
loop @@loop
pop ds
@@done:
mov Result, ax
{$ENDIF}
end;
end;

function UpdateCRC32(InitCRC: LongInt; var Buffer;
{$IFDEF Win32} Length: LongInt {$ELSE} Length: Word {$ENDIF}): LongInt;
begin
asm
{$IFDEF Win32}
push esi
push edi
push eax
push ebx
push ecx
push edx
lea edi, Crc32Tab
mov esi, Buffer
mov ax, word ptr InitCRC
mov dx, word ptr InitCRC + 2
mov ecx, Length
or ecx, ecx
jz @@done
@@loop:
xor ebx, ebx
mov bl, al
lodsb
xor bl, al
mov al, ah
mov ah, dl
mov dl, dh
xor dh, dh
shl bx, 1
shl bx, 1
add ebx, edi
xor ax, [ebx]
xor dx, [ebx + 2]
loop @@loop
@@done:
mov word ptr Result, ax
mov word ptr Result + 2, dx
pop edx
pop ecx
pop ebx
pop eax
pop edi
pop esi
{$ELSE}
push ds
pop es
push ds
lea di, CRC32Tab
lds si, Buffer
mov ax, word ptr InitCRC
mov dx, word ptr InitCRC + 2
mov cx, Length
or cx, cx
jz @@done
@@loop:
xor bh, bh
mov bl, al
lodsb
xor bl, al
mov al, ah
mov ah, dl
mov dl, dh
xor dh, dh
shl bx, 1
shl bx, 1
xor ax, es:[di + bx]
xor dx, es:[di + bx + 2]
loop @@loop
@@done:
pop ds
mov word ptr Result, ax
mov word ptr Result + 2, dx
{$ENDIF}
end;
end;

function FileCRC16(FileName: String; var CRC16: Word): Boolean; { Return True if ok }
var
f: File;
p: Pointer;
FSize: LongInt;
{$IFNDEF Win32}
tmp: Word;
{$ENDIF}
begin
{$I+}
try
AssignFile(f, FileName);
Reset(f, 1);
FSize := FileSize(f);
if FSize <> 0 then
begin
{$IFDEF Win32}
GetMem(p, FSize);
BlockRead(f, p^, FSize);
CRC16 := UpdateCrc16(0, p^, FSize); {!}
FreeMem(p, FSize);
{$ELSE}
CRC16 := 0; { Usualy from zero }
while FSize <> 0 do
begin
if FSize > $FFFF then tmp := $FFFF else tmp := FSize;
dec(FSize, tmp);
GetMem(p, tmp);
BlockRead(f, p^, tmp);
CRC16 := UpdateCrc16(Crc16, p^, tmp); {!}
FreeMem(p, tmp);
end;
{$ENDIF}

GetMem(p, 2); { Finish XModem crc with two nulls }
FillChar(p^, 2, 0);
Crc16 := UpdateCrc16(Crc16, p^, 2);
FreeMem(p, 2);

end;
Result := True;
except
Result := False;
end;
try
CloseFile(f);
except
end;
{$I-}
end;

function FileCRCArc(FileName: String; var CRCArc: Word): Boolean; { Return True if ok }
var
f: File;
p: Pointer;
FSize: LongInt;
{$IFNDEF Win32}
tmp: Word;
{$ENDIF}
begin
{$I+}
try
AssignFile(f, FileName);
Reset(f, 1);
FSize := FileSize(f);
if FSize <> 0 then
begin
{$IFDEF Win32}
GetMem(p, FSize);
BlockRead(f, p^, FSize);
CRCArc := UpdateCrcArc(0, p^, FSize); {!}
FreeMem(p, FSize);
{$ELSE}
CRCArc := 0; { Usualy from zero }
while FSize <> 0 do
begin
if FSize > $FFFF then tmp := $FFFF else tmp := FSize;
dec(FSize, tmp);
GetMem(p, tmp);
BlockRead(f, p^, tmp);
CRCArc := UpdateCrcArc(CrcArc, p^, tmp); {!}
FreeMem(p, tmp);
end;
{$ENDIF}
end;
Result := True;
except
Result := False;
end;
try
CloseFile(f);
except
end;
{$I-}
end;

function FileCRC32(FileName: String; var CRC32: LongInt): Boolean; { Return True if ok }
var
f: File;
p: Pointer;
FSize: LongInt;
{$IFNDEF Win32}
tmp: Word;
{$ENDIF}
begin
{$I+}
try
AssignFile(f, FileName);
Reset(f, 1);
FSize := FileSize(f);
if FSize <> 0 then
begin
{$IFDEF Win32}
GetMem(p, FSize);
BlockRead(f, p^, FSize);
CRC32 := UpdateCrc32($FFFFFFFF, p^, FSize); {!}
FreeMem(p, FSize);
{$ELSE}
CRC32 := $FFFFFFFF; { Usualy }
while FSize <> 0 do
begin
if FSize > $FFFF then tmp := $FFFF else tmp := FSize;
dec(FSize, tmp);
GetMem(p, tmp);
BlockRead(f, p^, tmp);
CRC32 := UpdateCrc32(Crc32, p^, tmp); {!}
FreeMem(p, tmp);
end;
{$ENDIF}
CRC32 := not CRC32; { Finish 32 bit crc by inverting all bits }
end;
Result := True;
except
Result := False;
end;
try
CloseFile(f);
except
end;
{$I-}

用它提供的DEMO和我另外一个在Torry下载的DEMO计算出来的结果不一样。

楼上shijunwu提供的程序我试过了，其中function UpdateCRCArc(InitCRC: Word; var
Buffer;Length:LongInt): Word;算出来的CRC跟我的算法算出来的CRC是一样的，其它两
个UpdateCRC16和UpdateCRC16算出来的结果不一样

我也计算过了，UpdateCRC16和我计算出来的不一样。
天哪～～怎么就这么复杂么？到底因为什么？？！！

肯定不是因为复杂，可能是算法或多项式的问题

根据CRC16的定义，多项式顶多是$1FFFF，所以，如果用$0001到$FFFF去计算，应该能猜出来的呀，
但是确猜不出来，奇怪。难道他效验码计算出来以后还经过了什么处理不成？！
今天问北京的总部的人了，他们说他们都是交给Microsoft去开发这些东西的，他们不知道细节，
我以为我真的笨得太狠了，结果我又问了另外一个人，你猜我听到了什么，“这个问题以前也出
现过，微软的人也提出多项式的效验有问题……”，晕……
但是，华为的人和郑州VCOM的人竟然基于同样的开放协议做了设备的联网，我KAO，真邪门～

有谁能找一份关于CRC的标准来看看？

见鬼，到国外的站点找来的程序算出来的竟然也不一样，难道都自称标准而一个标准的答案都没有吗？？？

可怜

好消息，这是厂家给的效验公式，但是我还没有能够算出和测量的数据相同的CRC值，请大家帮忙看看。
Here is the C code necessary to generate a CRC-16 CCiTT.

unsigned short CRC ( const char *buffer, int buflen )
{
unsigned crc = 0;
int q;

for ( int i = 0; i < buflen; i++ )
{
q = ( crc ^ buffer[ i ] &amp; 15;
crc = ( crc >> 4 ) ^ ( q * 4225 );
q = ( crc ^ ( buffer[ i ] >> 4 )) &amp; 15;
crc = ( crc >> 4 ) ^ ( q * 4225 );
}
return (unsigned short ) crc;
}

The packet format is as follows:

Byte |
Order: | DLE | STX | Command | Network ID | Zone ID | Sector ID | Data | DLE | ETX | CRC |
======|===================================================================|
Num of | 1 | 1 | 1 | 1 | 1 | 1 | [0 -128]| 1 | 1 | 2 |

The data transmission is big-endian (for smoke level the Hi byte is sent first followed by the Lo byte).

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