This kernel mode driver and Win32 library combination allow Win32 applications to execute IN and OUT instructions to the parallel port device hardware I/O ports.

Access is coordinated with the standard NT parallel driver to ensure that the parallel port is only 'claimed' if no other process is currently using it. Once the port is 'claimed', other processes are blocked from using the port (assuming they also use the standard parallel port arbitration scheme).

Once the application has finished using the parallel port, it may either exit or call the 'release' API and the parallel port is free for use by any other process again.

Do you have a DOS/Windows 16bit or Windows 95/98 32bit application that accesses a Parallel Port that you want to run under NT and you don't have the source?

Now, with one simple command, you can grant Parallel Port access to a specific application.

The program RUNAPP.EXE comes with the Direct I/O Access package and can be run to allow another application the Parallel Port.

To run a 32bit app use this command:

To run a 16bit app use this command:

The driver works by changing the I/O permission map (IOPM) for the process that 'claims' the indicated parallel port. Changing the IOPM, allows the process free access to the I/O port range of the parallel port hardware. It also supports additional parallel ports added using expansion cards.

The API calls are documented here:

Include the header file for definitions and function prototypes.

#include "ParllIo.h"

The GetParallelPortCount API returns the number of parallel ports present in the PC.

INT WINAPI GetParallelPortCount(VOID)

Return value:

The number of parallel ports present in the PC or 0 if none are present or an error occurred. For the specific error code, call the standard Win32 function GetLastError().

The GetParallelPortInfo API returns information about the a particular indicated parallel port, such as the physical I/O port address and number of I/O port addresses spanned by the hardware device.

BOOL WINAPI GetParallelPortInfo(
  DWORD        dwPort,
  PPARLLIOINFO pinfo)

Arguments:

	dwPort	specifies the parallel port for which information should be returned
	pinfo	specifies the address of a PARLLIOINFO structure defined below. The member dwParllIoInfoSize should be initialized on entry to size(PARLLIOINFO).

Return value:

TRUE if the function returns the port information or FALSE if the port does not exist or an error occurs. For the specific error code, call the standard Win32 function GetLastError().

typedef struct {
  // size of structure
  DWORD dwParllIoInfoSize;
  // address of parallel port
  DWORD dwPortAddress;
  // span of parallel port
  DWORD dwPortSpan;
} PARLLIOINFO, *PPARLLIOINFO;

The ClaimParallelPort API attempts to allocate the specified parallel port from the standard Windows NT parallel driver. A timeout may be specified to wait for the port to become free if already allocated. Additionally, either no wait may be specified or wait indefinitely.

BOOL WINAPI ClaimParallelPort(
  DWORD dwPort,
  DWORD dwTimeout)

Arguments:

	dwPort	specifies the parallel port to be claimed
	dwTimeout	specifies in milliseconds how long to wait for the parallel port if already owned by another process or INFINITE to wait indefinitely or 0 not to wait at all.

Return value:

TRUE if the function succeeds in claiming the parallel port specified or FALSE if it is in use or an error occurs. For the specific error code call the standard Win32 function GetLastError().

The ReleaseParallelPort API frees the parallel port for use by another process. Direct I/O should not be performed after this function is called. If this function is not called, the application will own the parallel port until the application exits or is terminated.

BOOL WINAPI ReleaseParallelPort(
  DWORD dwPort)

Arguments:

dwPort

specifies the parallel port to release

Return value:

TRUE if the function succeeds in releasing the parallel port specified or FALSE if the function fails or the process doesn't own the parallel port. For the specific error code call the standard Win32 function GetLastError().

For Visual Basic users six functions are provided for input and output as follows:

INT WINAPI OutByte(
  DWORD dwAdrs,
  INT   nByte)

INT WINAPI OutWord(
  DWORD dwAdrs,
  INT   nWord)

INT WINAPI OutDWord(
  DWORD dwAdrs,
  INT   nDWord)

INT WINAPI InByte(
  DWORD dwAdrs)

INT WINAPI InWord(
  DWORD dwAdrs)

INT WINAPI InDWord(
  DWORD dwAdrs)

The Direct I/O Access runtime package consists of two files, a kernel mode driver ParllIo.sys and a dynamic link library, ParllIo.dll. These files should be distributed with the application.

The driver may either be loaded on-demand or may be loaded when the system boots. If the driver is loaded on-demand, the user running the application must have NT administrator rights.

If it is envisiged that the user running the program will not have NT administrator rights, the driver can be installed to load at boot. NT administrator rights are still needed during setup, but once completed the driver can be used by non administrative users.

A setup program is provided to create the necessary registry entries to load the driver at boot. It can be run in quiet mode so that it can be called from the application setup program or in interactive mode.

If the driver will be loaded on-demand, the application setup program can copy the files into the application directory.

Running the command setup /h show the setup program options.

To perform a quiet mode installation from another setup program, run the following command setup c:\winnt /q.This will copy ParllIo.sys to the system32\drivers directory and ParllIo.dll to the system32 directory and make the necessary registry entries to load the driver on boot.

Alternatively, use the setup program in interactive mode as shown below. 

 

Note: A Windows 95/98 driver allowing coordinated access to parallel ports may be released if there is sufficient demand.