modbus asm pic
hi,
you can found modbus protocol at
www.modbus.org. it's open and i think there have few version of modbus including tcpip.
anyway, normally i'm only using two function to talk to modbus device. one is poll holding register (function code 03) write input register (function code 04 or 06, don't use this much). the crc generation is easy.
try this software Modbus Poll from
www.wittecom.com.
below is the crc generation write on delphi.
======= code ==========
const
cCRC16Table : TCRC16Table = (
$0000, $C0C1, $C181, $0140, $C301, $03C0, $0280, $C241,
$C601, $06C0, $0780, $C741, $0500, $C5C1, $C481, $0440,
$CC01, $0CC0, $0D80, $CD41, $0F00, $CFC1, $CE81, $0E40,
$0A00, $CAC1, $CB81, $0B40, $C901, $09C0, $0880, $C841,
$D801, $18C0, $1980, $D941, $1B00, $DBC1, $DA81, $1A40,
$1E00, $DEC1, $DF81, $1F40, $DD01, $1DC0, $1C80, $DC41,
$1400, $D4C1, $D581, $1540, $D701, $17C0, $1680, $D641,
$D201, $12C0, $1380, $D341, $1100, $D1C1, $D081, $1040,
$F001, $30C0, $3180, $F141, $3300, $F3C1, $F281, $3240,
$3600, $F6C1, $F781, $3740, $F501, $35C0, $3480, $F441,
$3C00, $FCC1, $FD81, $3D40, $FF01, $3FC0, $3E80, $FE41,
$FA01, $3AC0, $3B80, $FB41, $3900, $F9C1, $F881, $3840,
$2800, $E8C1, $E981, $2940, $EB01, $2BC0, $2A80, $EA41,
$EE01, $2EC0, $2F80, $EF41, $2D00, $EDC1, $EC81, $2C40,
$E401, $24C0, $2580, $E541, $2700, $E7C1, $E681, $2640,
$2200, $E2C1, $E381, $2340, $E101, $21C0, $2080, $E041,
$A001, $60C0, $6180, $A141, $6300, $A3C1, $A281, $6240,
$6600, $A6C1, $A781, $6740, $A501, $65C0, $6480, $A441,
$6C00, $ACC1, $AD81, $6D40, $AF01, $6FC0, $6E80, $AE41,
$AA01, $6AC0, $6B80, $AB41, $6900, $A9C1, $A881, $6840,
$7800, $B8C1, $B981, $7940, $BB01, $7BC0, $7A80, $BA41,
$BE01, $7EC0, $7F80, $BF41, $7D00, $BDC1, $BC81, $7C40,
$B401, $74C0, $7580, $B541, $7700, $B7C1, $B681, $7640,
$7200, $B2C1, $B381, $7340, $B101, $71C0, $7080, $B041,
$5000, $90C1, $9181, $5140, $9301, $53C0, $5280, $9241,
$9601, $56C0, $5780, $9741, $5500, $95C1, $9481, $5440,
$9C01, $5CC0, $5D80, $9D41, $5F00, $9FC1, $9E81, $5E40,
$5A00, $9AC1, $9B81, $5B40, $9901, $59C0, $5880, $9841,
$8801, $48C0, $4980, $8941, $4B00, $8BC1, $8A81, $4A40,
$4E00, $8EC1, $8F81, $4F40, $8D01, $4DC0, $4C80, $8C41,
$4400, $84C1, $8581, $4540, $8701, $47C0, $4680, $8641,
$8201, $42C0, $4380, $8341, $4100, $81C1, $8081, $4040);
function CalcCRC16(Buf
ointer; wLen:Integer):Word;
var nTemp : byte;
wCRCWord, dummy : word;
i : integer;
begin
wCRCWord := $FFFF;
for i:=1 to wLen-1 do
begin
dummy := pword(buf)^;
nTemp := PWord(buf)^ xor wCRCWord;
wCRCWord := (wCRCWord shl 8 ) OR (wCRCWord shr 8);
wCRCWord := wCRCWord xor cCRC16Table[nTemp];
Inc(PWord(Buf));
end;
result := wCRCWord;
end;
======== code ========
wisely