Low level serial and Parallel port access with Dark Basic Pro. tested and working with 5.7.

                                    ` This code was downloaded from The Game Creators
                                    ` It is reproduced here with full permission
                                    ` http://www.thegamecreators.com
                                    
                                    `###########################################################################################################
`  Serial and LPT Port Access
`  Uses Information Gathered from MSDN article 823179 and various parts of MSDN Knowledge base
`###########################################################################################################
#CONSTANT GENERIC_READ = 0x80000000
#CONSTANT GENERIC_WRITE = 0x40000000
#CONSTANT OPEN_EXISTING = 3
#CONSTANT FILE_ATTRIBUTE_NORMAL = 0x80
#CONSTANT NOPARITY = 0
#CONSTANT ONESTOPBIT = 0
#CONSTANT MAXDWORD = 4294967295
#CONSTANT SETXOFF =            1
` Simulate XOFF received
#CONSTANT SETXON  =            2
` Simulate XON received
#CONSTANT SETRTS  =            3
` Set RTS high
#CONSTANT CLRRTS  =            4
` Set RTS low
#CONSTANT SETDTR  =            5
` Set DTR high
#CONSTANT CLRDTR  =            6
` Set DTR low
#CONSTANT RESETDEV =           7
` Reset device if possible
#CONSTANT SETBREAK =           8
` Set the device break line.
#CONSTANT CLRBREAK =           9
` Clear the device break line.

#CONSTANT BUFFER_SIZE = 256

#CONSTANT KERNEL_DLL_ID = 1
#CONSTANT DCB_MEMBLOCK_ID = 1
#CONSTANT TIMEOUTS_MEMBLOCK_ID = 2
#CONSTANT IO_BUFFER_MEMBLOCK_ID = 3
#CONSTANT BYTES_READ_WRITE_ID = 4

Type T_DCB
   DCBlength as dword
   BaudRate as dword
   fBinary as dword
   fParity as dword
   fOutxCtsFlow as dword
   fOutcDsrFlow as dword
   fDtrControl as dword
   fDsrSensitivity as dword
   fTXContinueONXoff as dword
   fOutX as dword
   fInX as dword
   fErrorChar as dword
   fNull as dword
   fRtsControl as dword
   fAbortOnError as dword
   fDummy as dword
   XonLim as word
   XoffLim as word
   ByteSize as byte
   Parity as byte
   StopBits as byte
   XonChar as byte
   XoffChar as byte
   ErrorChar as byte
   EofChar as byte
   EvtChar as byte
   wReservedl as word
endtype

type T_COMMTIMEOUTS
   ReadIntervalTimeout as dword
   ReadTotalTimeoutMultiplier as dword
   ReadTotalTimeOutConstant as dword
   WriteTotalTimeoutMultiplier as dword
   WriteTotalTimeoutConstant as dword
endtype


`These Global variables will have to be inserted into you main source file
global hPort as dword
global DCB as T_DCB
global CommTimeouts as T_COMMTIMEOUTS
global Buffer as string
global Success as dword

`##########################################################################################################################
`  Initialization Driver
`##########################################################################################################################
Initialize_Serial_Driver()
`##########################################################################################################################
`  Initialize port
`##########################################################################################################################
hPort = CreateFile("COM1", GENERIC_READ || GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)
` Can use "COM2", "LPT1", etc...
print "Successfully open COM1!(Press any key to continue)"
wait key
print

`##########################################################################################################################
`  Get Current COM port Settings
`##########################################################################################################################
Success = GetCommState(hPort)
print "Successfully retrieved COM Settings!(Press any key to continue)"
print "Baud Rate :" ;DCB.BaudRate
print "ByteSize :";DCB.ByteSize
print "Parity :"; DCB.Parity
print "StopBits :";DCB.StopBits
wait key
print

`##########################################################################################################################
`  Change Com Port Settings
`##########################################################################################################################
DCB.BaudRate = 9600
DCB.ByteSize = 8
DCB.Parity = NOPARITY
DCB.StopBits = ONESTOPBIT
Success = SetCommState(hPort)
print "Successfully Set COM port values!(Press any key to continue)"
wait key
print

`#########################################################################################################################
`  Get COM port Settings (again)
`#########################################################################################################################
Success = GetCommState(hPort)
print "Successfully retrieved COM Settings!(Press any key to continue)"
print "Baud Rate :" ;DCB.BaudRate
print "ByteSize :";DCB.ByteSize
print "Parity :"; DCB.Parity
print "StopBits :";DCB.StopBits
wait key
print

`########################################################################################################################
`  Get COM port Timeouts
`########################################################################################################################
Success = GetCommTimeouts(hPort)
print "Successfully retrieved COM Timeouts!(Press any key to continue)"
print "ReadIntervalTimeout = "; CommTimeouts.ReadIntervalTimeout
print "ReadTotalTimeoutConstant = "; CommTimeouts.ReadTotalTimeoutConstant
print "ReadTotalTimeoutMultiplier = "; CommTimeouts.ReadTotalTimeoutMultiplier
print "WriteTotalTimeoutConstant = "; CommTimeouts.WriteTotalTimeoutConstant
print "WriteTotalTimeoutMultiplier = ";CommTimeouts.WriteTotalTimeoutMultiplier
wait key
print

`########################################################################################################################
`  Set COM port Timeouts
`########################################################################################################################
CommTimeouts.ReadIntervalTimeout = 100
CommTimeouts.ReadTotalTimeoutConstant = 3000 :`In Milliseconds
CommTimeouts.ReadTotalTimeoutMultiplier = 0
CommTimeouts.WriteTotalTimeoutConstant = 1000
CommTimeouts.WriteTotalTimeoutMultiplier = 0
Success = SetCommTimeouts(hPort)
print "Successfully set COM Timeouts!(Press any key to continue)"
wait key
print

`########################################################################################################################
`  Get COM port Timeouts
`########################################################################################################################
Success = GetCommTimeouts(hPort)
print "Successfully retrieved COM Timeouts!(Press any key to continue)"
print "ReadIntervalTimeout = "; CommTimeouts.ReadIntervalTimeout
print "ReadTotalTimeoutConstant = "; CommTimeouts.ReadTotalTimeoutConstant
print "ReadTotalTimeoutMultiplier = "; CommTimeouts.ReadTotalTimeoutMultiplier
print "WriteTotalTimeoutConstant = "; CommTimeouts.WriteTotalTimeoutConstant
print "WriteTotalTimeoutMultiplier = ";CommTimeouts.WriteTotalTimeoutMultiplier
wait key
print

`########################################################################################################################
`  Clear DTR
`########################################################################################################################
Success = EscapeCommFunction(hPort,CLRDTR)
print "Successfully cleared DTR!(Press any key to continue)"
wait key
print

`#######################################################################################################################
`  Read From Serial Port
`#######################################################################################################################
print "Reading from Serial Port...Please wait."
repeat
success = ReadFile(hPort, BUFFER_SIZE - 1)
print "Serial in Data (Press ENTER to continue): "; buffer
until returnkey()
print

`######################################################################################################################
`  Write To Serial Port
`######################################################################################################################
buffer = "Hello!"
repeat
success = WriteFile(hPort, len(buffer))
print "Serial out Data (Press space to continue): ";buffer
until spacekey()
print

`#######################################################################################################################
`  Close the COM port
`#######################################################################################################################
Success = CloseHandle(hPort)
print "Done!"
wait key

Cleanup_Memory()
end


`#######################################################################################################################
`  Internal Functions
`#######################################################################################################################
function Initialize_Serial_Driver()

load dll "\windows\system32\kernel32.dll", KERNEL_DLL_ID

if dll exist(KERNEL_DLL_ID) = 0
   Print "Could not find kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "CreateFileA") = 0
   Print "Could not find CreateFile command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "GetCommState") = 0
   Print "Could not find GetCommState command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "SetCommState") = 0
   Print "Could not find SetCommState command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "GetCommTimeouts") = 0
   Print "Could not find GetCommTimeouts command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "SetCommTimeouts") = 0
   Print "Could not find SetCommTimeouts command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "ReadFile") = 0
   Print "Could not find ReadFile command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "WriteFile") = 0
   Print "Could not find WriteFile command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "CloseHandle") = 0
   Print "Could not find CloseHandle command in kernel32.dll"
   wait key
   end
endif

if dll call exist(KERNEL_DLL_ID, "EscapeCommFunction") = 0
   Print "Could not find EscapeCommFunction command in kernel32.dll"
   wait key
   end
endif

Make memblock DCB_MEMBLOCK_ID, 80 : ` For DCB
Make memblock TIMEOUTS_MEMBLOCK_ID, 20 : ` For TimeOuts
Make memblock IO_BUFFER_MEMBLOCK_ID, BUFFER_SIZE : `I/O buffer
Make memblock BYTES_READ_WRITE_ID, 4 : `Bytes Written or Read
endfunction

function CreateFile(lpFileName as String, dwDesiredAccess as Dword, dwShareMode as dword, lpSecurityAttributes as dword, dwCreationDisposition as Dword, dwFlagsAndAttributes as dword, hTemplateFile as Dword)
ret = call dll (KERNEL_DLL_ID, "CreateFileA",lpFilename, dwDesiredAccess, dwShareMode, lpSecurityAttributes, dwCreationDisposition, dwFlagsAndAttributes, hTemplateFile)
if ret = -1
   Print "Could not retrieve handle for COM port.(Is something else using the Port?)"
   wait key
   end
endif
endfunction ret

function GetCommState(nCid as dword)
ret = call dll (KERNEL_DLL_ID, "GetCommState", nCid, get memblock ptr(DCB_MEMBLOCK_ID))
if ret = 0
   print "Could not get Com port state"
   wait key
   end
endif
   DCB.DCBlength  = memblock dword(DCB_MEMBLOCK_ID,0)
   DCB.BaudRate  = memblock dword(DCB_MEMBLOCK_ID,4)
   DCB.fBinary  = memblock dword(DCB_MEMBLOCK_ID,8)
   DCB.fParity  = memblock dword(DCB_MEMBLOCK_ID,12)
   DCB.fOutxCtsFlow  = memblock dword(DCB_MEMBLOCK_ID,16)
   DCB.fOutcDsrFlow  = memblock dword(DCB_MEMBLOCK_ID,20)
   DCB.fDtrControl  = memblock dword(DCB_MEMBLOCK_ID,24)
   DCB.fDsrSensitivity  = memblock dword(DCB_MEMBLOCK_ID,28)
   DCB.fTXContinueONXoff  = memblock dword(DCB_MEMBLOCK_ID,32)
   DCB.fOutX  = memblock dword(DCB_MEMBLOCK_ID,36)
   DCB.fInX  = memblock dword(DCB_MEMBLOCK_ID,40)
   DCB.fErrorChar  = memblock dword(DCB_MEMBLOCK_ID,44)
   DCB.fNull  = memblock dword(DCB_MEMBLOCK_ID,48)
   DCB.fRtsControl  = memblock dword(DCB_MEMBLOCK_ID,52)
   DCB.fAbortOnError  = memblock dword(DCB_MEMBLOCK_ID,56)
   DCB.fDummy  = memblock dword(DCB_MEMBLOCK_ID,60)
   DCB.XonLim  = memblock word(DCB_MEMBLOCK_ID,64)
   DCB.XoffLim  = memblock word(DCB_MEMBLOCK_ID,66)
   DCB.ByteSize  = memblock byte(DCB_MEMBLOCK_ID,68)
   DCB.Parity  = memblock byte(DCB_MEMBLOCK_ID,69)
   DCB.StopBits  = memblock byte(DCB_MEMBLOCK_ID,70)
   DCB.XonChar  = memblock byte(DCB_MEMBLOCK_ID,71)
   DCB.XoffChar  = memblock byte(DCB_MEMBLOCK_ID,72)
   DCB.ErrorChar  = memblock byte(DCB_MEMBLOCK_ID,73)
   DCB.EofChar  = memblock byte(DCB_MEMBLOCK_ID,74)
   DCB.EvtChar  = memblock byte(DCB_MEMBLOCK_ID,75)
   DCB.wReservedl  = memblock word(DCB_MEMBLOCK_ID,76)
endfunction ret

function SetCommState(nCid as dword)
   Write memblock dword DCB_MEMBLOCK_ID,0,DCB.DCBlength
   Write memblock dword DCB_MEMBLOCK_ID,4,DCB.BaudRate
   Write memblock dword DCB_MEMBLOCK_ID,8,DCB.fBinary
   Write memblock dword DCB_MEMBLOCK_ID,12,DCB.fParity
   Write memblock dword DCB_MEMBLOCK_ID,16,DCB.fOutxCtsFlow
   Write memblock dword DCB_MEMBLOCK_ID,20,DCB.fOutcDsrFlow
   Write memblock dword DCB_MEMBLOCK_ID,24,DCB.fDtrControl
   Write memblock dword DCB_MEMBLOCK_ID,28,DCB.fDsrSensitivity
   Write memblock dword DCB_MEMBLOCK_ID,32,DCB.fTXContinueONXoff
   Write memblock dword DCB_MEMBLOCK_ID,36,DCB.fOutX
   Write memblock dword DCB_MEMBLOCK_ID,40,DCB.fInX
   Write memblock dword DCB_MEMBLOCK_ID,44,DCB.fErrorChar
   Write memblock dword DCB_MEMBLOCK_ID,48,DCB.fNull
   Write memblock dword DCB_MEMBLOCK_ID,52,DCB.fRtsControl
   Write memblock dword DCB_MEMBLOCK_ID,56,DCB.fAbortOnError
   Write memblock dword DCB_MEMBLOCK_ID,60,DCB.fDummy
   Write memblock word DCB_MEMBLOCK_ID,64,DCB.XonLim
   Write memblock word DCB_MEMBLOCK_ID,66,DCB.XoffLim
   Write memblock byte DCB_MEMBLOCK_ID,68,DCB.ByteSize
   Write memblock byte DCB_MEMBLOCK_ID,69,DCB.Parity
   Write memblock byte DCB_MEMBLOCK_ID,70,DCB.StopBits
   Write memblock byte DCB_MEMBLOCK_ID,71,DCB.XonChar
   Write memblock byte DCB_MEMBLOCK_ID,72,DCB.XoffChar
   Write memblock byte DCB_MEMBLOCK_ID,73,DCB.ErrorChar
   Write memblock byte DCB_MEMBLOCK_ID,74,DCB.EofChar
   Write memblock byte DCB_MEMBLOCK_ID,75,DCB.EvtChar
   Write memblock word DCB_MEMBLOCK_ID,76,DCB.wReservedl
ret = call dll (KERNEL_DLL_ID, "SetCommState", nCid, get memblock ptr(DCB_MEMBLOCK_ID))

if ret = 0
   print "Could not set Com port state"
   wait key
   end
endif

endfunction ret

function GetCommTimeouts(nCid as dword)
ret = call dll (KERNEL_DLL_ID, "GetCommTimeouts", nCid, get memblock ptr(TIMEOUTS_MEMBLOCK_ID))
if ret = 0
   print "Could not get Com Timeouts."
   wait key
   end
endif
   CommTimeouts.ReadIntervalTimeout = memblock dword(TIMEOUTS_MEMBLOCK_ID,0)
   CommTimeouts.ReadTotalTimeoutMultiplier = memblock dword(TIMEOUTS_MEMBLOCK_ID,4)
   CommTimeouts.ReadTotalTimeOutConstant = memblock dword(TIMEOUTS_MEMBLOCK_ID,8)
   CommTimeouts.WriteTotalTimeoutMultiplier = memblock dword(TIMEOUTS_MEMBLOCK_ID,12)
   CommTimeouts.WriteTotalTimeoutConstant = memblock dword(TIMEOUTS_MEMBLOCK_ID,16)
endfunction ret

function SetCommTimeouts(nCid as dword)
   Write memblock dword TIMEOUTS_MEMBLOCK_ID,0,CommTimeouts.ReadIntervalTimeout
   Write memblock dword TIMEOUTS_MEMBLOCK_ID,4,CommTimeouts.ReadTotalTimeoutMultiplier
   Write memblock dword TIMEOUTS_MEMBLOCK_ID,8,CommTimeouts.ReadTotalTimeOutConstant
   Write memblock dword TIMEOUTS_MEMBLOCK_ID,12,CommTimeouts.WriteTotalTimeoutMultiplier
   Write memblock dword TIMEOUTS_MEMBLOCK_ID,16,CommTimeouts.WriteTotalTimeoutConstant
ret = call dll (KERNEL_DLL_ID, "SetCommTimeouts", nCid, get memblock ptr(TIMEOUTS_MEMBLOCK_ID))

if ret = 0
   print "Could not set Com Timeouts."
   wait key
   end
endif

endfunction ret

function WriteFile(hFile as dword, nNumberOfBytesToWrite as dword)
if len(Buffer) > BUFFER_SIZE then Buffer = left$(Buffer,BUFFER_SIZE)
for i = 1 to len(buffer)
   write memblock byte IO_BUFFER_MEMBLOCK_ID,i-1,asc(mid$(buffer,i))
next i
ret = call dll(KERNEL_DLL_ID, "WriteFile", hfile, get memblock ptr(IO_BUFFER_MEMBLOCK_ID), nNumberOfBytesToWrite, get memblock ptr(BYTES_READ_WRITE_ID),0)
if ret = 0
   print "Could not write to com port."
   wait key
endif

endfunction ret

function ReadFile(hFile as dword, nNumberOfBytesToRead as dword)
ret = call dll(KERNEL_DLL_ID, "ReadFile", hfile, get memblock ptr(IO_BUFFER_MEMBLOCK_ID), nNumberOfBytesToRead, get memblock ptr(BYTES_READ_WRITE_ID),0)
if ret = 0
   print "Could not read from com port."
   wait key
endif
buffer = ""
for i = 0 to memblock dword(BYTES_READ_WRITE_ID,0) - 1
   buffer = buffer + chr$(memblock byte(IO_BUFFER_MEMBLOCK_ID,i))
next i
endfunction ret

function CloseHandle(hObject as dword)
ret = call dll(KERNEL_DLL_ID, "CloseHandle", hObject)
if ret = 0
   print "Could not close handle."
   wait key
   end
endif
endfunction ret

function EscapeCommFunction(hFile as dword, dwFunc as dword)
ret = call dll(KERNEL_DLL_ID, "EscapeCommFunction", hFile, dwFunc)
if ret = 0
   Print "EscapeCommFunction Failed."
   wait key
   end
endif
endfunction ret

function Cleanup_Memory()
   delete memblock DCB_MEMBLOCK_ID
   delete memblock TIMEOUTS_MEMBLOCK_ID
   delete memblock IO_BUFFER_MEMBLOCK_ID
   delete memblock BYTES_READ_WRITE_ID
   delete dll KERNEL_DLL_ID
endfunction