I need use Windows API control the serial port,But I don,t know,What,s Wrong transmit data unsuccess.

This is my Code:

#DEFINE GENERIC_READ 0x80000000
#DEFINE GENERIC_WRITE 0x40000000
#DEFINE OPEN_EXISTING 3
#DEFINE FILE_FLAG_OVERLAPPED 0x40000000

DECLARE INTEGER CreateFile IN kernel32;
STRING lpFileName, INTEGER dwDesiredAccess, INTEGER dwShareMode,;
INTEGER lpSecurityAttributes, INTEGER dwCreationDisposition,;
INTEGER dwFlagsAndAttributes, INTEGER hTemplateFile

DECLARE INTEGER CloseHandle IN kernel32 INTEGER hObject

DECLARE INTEGER WriteFile IN kernel32 INTEGER hFile,;
STRING @ lpBuffer,INTEGER nBt2Write,INTEGER @ lpBtWritten,INTEGER lpOverlapped

DECLARE INTEGER ReadFile IN kernel32 INTEGER hFile,;
STRING @ lpBuffer,INTEGER nNumberOfBytesToRead,INTEGER @ lpNumberOfBytesRead, INTEGER lpOverlapped

ICDEV = CreateFile('COM1', GENERIC_READ+GENERIC_WRITE, 0,0,;
OPEN_EXISTING, FILE_FLAG_OVERLAPPED, 0)

outdata=chr(65)+chr(66)+chr(67)
indata=space(6)
LOCAL j,p
j=0

&&What,s wrong WriteFile unsuccess
a=WriteFile(ICDEV,@OUTDATA,3,@j,0)

b=ReadFile(ICDEV,@indata,3,@j,0)

= CloseHandle(ICDEV)