February 1, 1995 Hayes Tech Tip -- Installing a Hayes Internal Modem --------------------------------------------------- When you install an internal modem, you must assign it a unique COM port setting. If your modem is set to use a COM port that is being used by another device, you may experience COM port or interrupt conflicts. Symptoms of COM Port and Interrupt Conflicts: The communication software cannot find the modem. Your PC locks up when accessing the modem The modem doesn't respond to AT commands. The modem works in some applications, but not in others. The modem used to work, but doesn't anymore. The serial mouse doesn't function properly. top Standard COM Port Assignments The COM port that you select for your modem specifies an address and IRQ setting. The address tells your computer where to find your modem, just like a street address. The IRQ setting is used by your modem to get your computers attention. The table below outlines the standard address and interrupt settings for each COM port. COM Port Address Interrupt ------------------------------------------------------ COM1 03F8 IRQ4 COM2 02F8 IRQ3 COM3 03E8 IRQ4 COM4 02E8 IRQ3 Resolving Interrupt Conflicts COM port or interrupt conflicts can be resolved by selecting a unique COM port setting for the modem. There are several steps you can take to prevent COM port conflicts. top Identifying Serial Ports Already Being Used In Your Computer First, it is a good idea to determine how many serial ports are on the PC without the modem installed. You should refer to the manual or documentation for your computer to find information regarding serial port addresses and IRQ assignments. This information will give you an indication of which addresses and IRQs are already being used by your system. Most computers have one serial port configured as COM1 and have COM2 unconfigured. This setup will allow you to select COM2 for the internal modem since it is not in use by the system. However, if your system has two serial ports, COM1 and COM2 before you install the modem, you will not be able to install the modem on any of the standard serial ports. You will not be able to select COM3 or COM4 because they share the IRQs with COM1 and COM2. There are two solutions to this type of problem. Solution 1: Disabling Serial Ports topThe first solution is to refer to your computer documentation for directions on disabling one of the serial ports. If you disable COM2 in your systemAs configuration, you will be able to select COM2 for the internal modem. Solution 2: Selecting Non-Standard Interrupts The second solution is to select a non-standard interrupt setting for the modem such as IRQ2, IRQ5, IRQ9, or IRQ15. You should find information in your modem documentation on how to select non-standard IRQs. In situations where nonstandard IRQs are needed, IRQ5 is usually recommended since most computers do not use IRQ5. However, some devices such as sound cards, network cards, a second parallel port, CD-ROM interface cards, tape backup interface cards, SCSI interface cards, and scanner interface cards can use IRQ5. If one of these cards is installed in your computer, check the IRQ level of that card before selecting IRQ5 for the internal modem. If IRQ5 is being used, you can change the IRQ level of that card and select IRQ5 for the modem. Configuring Windows Programs If you are using Windows, advanced settings for serial ports can be topfound in the Control Panel. Changes made in Control Panel apply to all Windows- based communications programs. Once configured in Control Panel, you may select the COM port in the communication application without having to change the IRQ level in the program. Configuring Your Communications Software After you have determined which COM port will be used for the modem, you must configure your software to the communications port and IRQ level in which you have selected for the modem. If you have selected a nonstandard interrupt for the modem, you must configure your communications software with the proper settings to find the modem. Normally there is an advanced installation or port assignment screen where you can change the address and IRQ level of serial ports (Some DOS-based programs does not have this feature). Contacting Hayes Customer Service If, after reading through this Tech Tip and trying the recommended solutions, you are still unable to isolate or resolve a problem, contact Hayes Customer Service at the following numbers: top World Headquarters Tel. 404/441-1617 Fax 404/449-0087 Hayes Online BBS 404/446-6336 Asia Pacific (Hong Kong) Tel. 011-852-887-1037 Fax 011-852-887-7548 Hayes Online BBS 011-852-887-7590 Europe Tel. 011-44-252-775544 Fax 011-44-252-775511 Hayes Online BBS 011-44-252-775599 Hayes is a trademark of Hayes Microcomputer Products, Inc. Other trademarks mentioned are the property of their respective companies. Copyright 1995 Hayes Microcomputer Products, Inc. All rights reserved.