COM Port Conflicts.

Most PCs will allow up to four COM ports at the settings shown in Table 1 below. The unfortunate situation is that ports 1 and 3 share the same interrupt (IRQ 4) and ports 2 and 4 also share the same interrupt (IRQ 3). Placing devices which use the interrupts on either of these pair of COM ports will prevent one or both devices from operating properly. For instance, having a serial mouse on COM 1 and the DECtalk Express on COM 3 will probably mean that one or both of these options will not work correctly or at all. The same holds true for devices on COM 2 and COM 4.

Table 1. - Serial COM Port Settings

COM port | I/O Address | IRQ
COM1 | 3F8 | 4
COM2 | 2F8 | 3
COM3 | 3E8 | 4
COM4 | 2E8 | 3

Avoiding COM Port Conflicts.

Devices may be attached to these pairs of COM ports (COM1/COM3 and COM2/COM4) if one of the devices can support the setting of a non-standard IRQ setting. Usually COM port 1 and most times COM port 2 are part of the system board and may not support non-standard settings. For instance, if a serial mouse is attached to COM 1 (IRQ 4) then an internal modem card can bet set to use COM3 but with a non-standrad IRQ of 5. A similar situation could be to have the DECtalk Express use the standard settings for COM 2 (IRQ 3) and have an internal modem use COM 4 but with and IRQ of 5.

Checking COM Port Configuration.

If the Installation program cannot find a DECtalk Express on a standard COM port or at the COM port settings you specified, it recommended that you use the COMCHK utility program to identify which COM port the DECtalk Express is connected to.

Run the program by typing COMCHK and press the Enter key. The program will check the four standard COM port I/O address' in a PC for an operating DECtalk Express. The utility will report the results of its tests on the PC monitor. The message "DECtalk Express found on Com port X", where "X" is the com port number, will be spoken when an operational DECtalk Express is found. If the unit is found by the utility, then a Custom installation can be tried using the COM port and IRQ the unit was found on as the answer to the questions "Which com port ." and "Which IRQ." A beep will sound from the PC speaker if an operating DECtalk Express is not found on any of the COM ports.

If the COMCHK utility does not find a DECtalk Express on Com ports 1-4 then other utilities can be used to try to identify the COM ports in your system and their respective settings.

NOTE: The Installation program sets the DECtalk Express batch file to remove the system resources used by the DECtalk Express from the system inventory. This is done to try to prevent conflict with other devices which may also try to use the same resources. System utility programs like MSD.EXE which check COM port settings will then no longer show any resources for that specific COM port. The resources are returned to normal when the system is rebooted and the DECtalk driver is not loaded. If an application communicates directly with the Express e.g. the driver DT_DRIV.EXE is not loaded, running the Express batch file will prevent the application from finding the Express until the system is reset.

Identifying Conflicting Devices.

If the TSR still fails to load, then it may be necessary to temporarily remove other options that use the COM ports like internal modems, serial mice, etc. until a satisfactory installation is made. Once the conflicting device is identified, then adjustments in the systems resources utilized will have to be made to resolve them. The paragraph above titled "Avoiding COM Port Conflicts" can be used as a basis for resolving the resource conflict.

Changing Serial Port Configuration.

The easiest way to change the COM port settings for the DECtalk Express driver is to rerun the Installation program and select the Custom installation. The Custom installation provides the ability to select a standard COM port number or to select a COM port at a non-standard IRQ number.

Alternatively, the parameters can be changed by editing the DTEXP.BAT file which is located in the default DECtalk Express directory, DTEXP, or in the directory that you specified during installation. To change the communications port parameters, at the DOS prompt, do the following:

1. Edit the DT_DRIV command string in the file DTEXP.BAT. The Default Install program puts this file in the DTEXP subdirectory.

2. Find the line which reads DT_DRIV -C -b 3f8 -I 4.

NOTE: the "-b" and "-I" settings may differ from those that are shown here.

3. Change the port parameters using the serial port settings listed in the above serial COM port settings table or to the non- standard settings of the I/O device you are using.

For example, to change the physical communications port to COM3, the base address to 3E8 and the IRQ to 5 you would type the following:

DT_DRIV -C (space) -b (space) 3E8 (space) -I (space) 5

The COPY command trapping of the pseudo COM4 will remain unchanged.

NOTE: These base I/O address and IRQ settings must match the settings on the communications option installed in your PC.

4. Save the changes to the file.

5. Type DTEXP and press the Enter key.

The system will attempt to load the DECtalk Express TSR with the newly specified settings. The DECtalk Express will now speak its "DECtalk Express is connected to.... ." if all of the COM settings are correct.