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T A N D E M Rev. 3.1 Copyright (C) 1988 - Louis E. Wheeler All Rights Reserved WARRANTY The TANDEM Remote System is warranted to be free from copying defects when shipped. There are no other warranties, expressed or implied, including, but not limited to, any implied warranties of merchantability or fitness for any particular application. In no event will Louis E. Wheeler be liable for consequential damages even if advised of the possibility of such damages. This software has been thoroughly tested, but there may be bugs for which Louis E. Wheeler cannot be held responsible. No liability or responsibility is assumed to the customer or any other person or organization for any application or use of this software or documentation sold or distributed by Louis E. Wheeler or any dealer. N O T I C E THE TANDEM REMOTE SYSTEM IS NOT PUBLIC DOMAIN SOFTWARE Table of Contents The TANDEM Remote System . . . . . . . . . 1 Equipment Requirements . . . . . . . . . . 2 Host Computer . . . . . . . . . . . . . 2 Remote Computer . . . . . . . . . . . . 2 Modem . . . . . . . . . . . . . . . . . 2 Cables . . . . . . . . . . . . . . . . 2 Getting Started . . . . . . . . . . . . . 4 Passwords . . . . . . . . . . . . . . . . 7 Operating TANDEM . . . . . . . . . . . . . 8 From A "Remote" Location . . . . . . . 8 CLS . . . . . . . . . . . . . . . . 9 TYPE . . . . . . . . . . . . . . . . 9 DOS . . . . . . . . . . . . . . . . 9 BYE . . . . . . . . . . . . . . . . 9 SHUTDOWN . . . . . . . . . . . . . . 9 Extended Commands . . . . . . . . . . . 10 LDIR . . . . . . . . . . . . . . . . 10 LDOS . . . . . . . . . . . . . . . . 10 CHAT . . . . . . . . . . . . . . . . 10 SEND . . . . . . . . . . . . . . . . 10 From The "Host" Console . . . . . . . . 12 From A "Remote" Terminal . . . . . . . 12 When Directly Connected By Cable . . . 12 Problem Programs . . . . . . . . . . . . . 13 In Case of Difficulty . . . . . . . . . . 14 User Support . . . . . . . . . . . . . . 15 The TANDEM Remote System Rev. 3.1 Tandem adj. 1: consisting of things or having parts arranged one behind the other 2: work- ing in conjunction with each other. - Webster's New Collegiate Dictionary Two computers linked together with the TANDEM Remote System work in conjunction with each other. Both monitors present the same information, both keyboards can be used to run programs and enter data. The TANDEM Remote System does what most other modem programs cannot do; it allows you to run virtually all PC-DOS software from a remote site. You can even run those pesky programs that bypass the operating system and write directly to the video memory. TANDEM does what the CTTY command and other modem program SHELL or GATEWAY commands promise, but fail to deliver. The TANDEM system is designed to operate with "Hayes" compatible modems, or, if you wish, two computers can be directly connected using an RS- 232C "null modem" cable. It is also possible to substitute an H/Z-19 terminal for the "remote" computer, however, the number of application that can be operated from a terminal is limited. The software consists of two separate modules: (1) the TANDEM.EXE program that runs on the "host" computer, and (2) the TMODEM.EXE program that runs on the "remote" computer. It is the "host" computer that actually executes the application and updates the files, your office computer for example. At some "remote" location, say your home, or another office, a second computer running the TMODEM.EXE program will enable to you to control the "host" computer almost as though you were actually sitting in front of the "host" console. However, there are some limitations on what TANDEM can do. Because of the relatively slow transfer of information from the host to the remote computer, it does not work well with programs that use animation. And, because the TMODEM.EXE program is especially designed to work with TANDEM.EXE, it cannot be used as a general purpose modem program to access bulletin board systems (BBS), or other information retrieval services. The following pages describe the operation of the TANDEM Remote System in detail. 1 EQUIPMENT HOST COMPUTER The "host" is an IBM compatible computer with at least one serial port, either COM1 or COM2 (or internal modem), and at least 256K bytes of memory, 640K bytes is suggested. Computers running at 4.77 MHz will work, but over all performance is greatly enhanced with computers running at 6 MHz or faster. Either color (CGA) or monochrome (MDA) video controller cards are acceptable. Enhanced Graphics adapter (EGA) cards will work, but programs must use the CGA or MDA modes. Any monitor (color or monochrome) compatible with the video controller can be used. A monitor with an integral power switch is useful, as the monitor can then be turned off when the host computer is left unattended. REMOTE COMPUTER The "remote" is an IBM compatible computer or H/Z-19 terminal. A remote computer should have at least 256K bytes of memory and one serial port (or internal modem). Computers running at 4.77 MHz work just fine, even small portables can be used. The video system can be either color or monochrome. Note that the "remote" computer can use a monochrome monitor, even though the "host" computer uses color; the opposite is also true. MODEM A "Hayes" compatible modem that uses the "AT" command set and responds with the standard Hayes command responses is required. Modems operating at 300-baud will work but the results may be disappointing. A 1200-baud modem works well with most programs, but modems capable of even higher baud rates are useful when running some applications. However, some computers running at 4.77 MHz do not have the "horse power" to handle modems running faster than 1200-baud. CABLES Modem cables only need three signal lines, "hand shake" signals are set to a "high" state and then ignored. RS-232C pin connections are as follows: Pin Name Signal 2 TxD Transmitted Data 3 RxD Received Data 7 Gnd Signal Ground 2 RS-232C cables used for direct connection differ from those used to connect a modem to a computer and are normally referred to as a "Null Modem" cable. In this type of cable, pin 2 (Transmitted Data) on one end of the cable is connected to pin 3 (Received Data) on the other end of the cable. That is, pins 2 and 3 are cross connected. Signal ground is connected to pin 7 on both ends of the cable. TANDEM does not use the "hand shake" signals and they may be left unconnected. 3 GETTING STARTED We suggest that you first format two (2) diskettes. Run the FORMAT program with the /S option to produce a diskette with system files. Copy your original TANDEM diskette onto one of these newly formatted diskettes with the operating system COPY command, then place your original TANDEM diskette in a place for safe keeping. Next, make a second copy of the TANDEM diskette from the copy you have just made. One copy of the TANDEM system is for use on the "host" computer, the other is for the "remote" computer. Both of the diskettes should now have the following files: COMMAND.COM Disk Operating System. TANDEM.EXE The host program. TMODEM.EXE The remote modem program. PASSWRDS.DAT Sample pass word file. TANDEM.DOC Instruction manual. READ.ME A note to the user. If you wish, you can delete TANDEM.DOC and the READ.ME files from the diskettes using the operating system DEL or ERASE commands. Only the COMMAND.COM, TANDEM.EXE, and PASSWRDS.DAT files are required for the host (main computer) system. Only COMMAND.COM and TMODEM.EXE are required for the remote computer system. However, creating three "batch" files, an AUTOEXEC.BAT, HOST.BAT, and REMOTE.BAT, will make it even easier to start the TANDEM system and provide for an automatic re- start in case of a power failure when the host computer is left unattended. Before creating the three "batch" files, some information is required. You will need to know: (1) the serial port number (COM1 or COM2) you are going to use on the host and remote computers; (2) the baud rate at which your modems, or serial ports, are going to operate; (3) whether the computers are to be connected by modems, or directly connected with an RS-232C cable; (4) if you are using a modem, the dialing method to be used (pulse or tone); (5) whether your remote is to be a computer running TMODEM or an H/Z-19 terminal. Creation of the "batch" files is optional, but you still need to know the system configuration. If you run TANDEM or TMODEM without supplying this information on the command line, you will be asked to furnish it before communication can be established between the two computers (or host computer and terminal). 4 The TANDEM command line is constructed as follows: d:>TANDEM port, baud-rate [,H] [,D] port Is the COM port number, 1 or 2. baud-rate Is the baud rate at which the modem/port runs. H The optional "H" indicates that the remote is an H/Z-19 terminal. Default is a computer. D The optional "D" indicates that the two computers are directly connected via cable. Default is a connection via modems. For example, to invoke TANDEM from the operating system prompt, using COM port #2, at 1200-baud, with a remote computer, using a modem, the command line would look like this: A:>TANDEM 2, 1200 Using COM port #1, at 2400-baud, with an H-19 terminal, connected to the serial port with an RS-232C cable would look like this: A:>TANDEM 1, 2400, H, D Note: the spaces between parameters are optional, however, the commas separating the fields are required. The TMODEM command line is similar to the TANDEM command line. It is constructed as follows: d:>TMODEM port, baud-rate [,P] [,D] port Is the serial port number. baud-rate Is the baud rate of the serial port/modem. P The optional "P" indicates that pulse dialing rather than tone dialing is to be used. Default is tone dialing. D The optional "D" indicates that the two computers are directly connected via cable. Default is a connection via modems. For example, using COM port #1, at 1200-baud, with tone dialing, via modem: A:>TMODEM 1, 1200 Using COM port #2, at 2400-baud, with pulse dialing: A:>TMODEM 2, 2400, P Using COM port #1, at 9600-baud, directly connected via RS-232C cable (Note: dialing method is not applicable when directly connected): A:>TMODEM 1, 9600, D 5 As with the TANDEM example, spaces between parameters are optional, but commas are required to separate fields. Using the same command line format, we can now generate a "batch" file called HOST.BAT. This file can be created with an ASCII text editor or using the operating system COPY command. To create HOST.BAT using the COPY command, enter the following: A:>COPY CON: HOST.BAT TANDEM 2, 1200, H, D ^Z <RETURN> The symbol ^Z is entered by pressing the "Z" key while holding down the "Control" key. Refer to the DOS manual for additional information on creating "batch" files using the COPY command. Using the same procedure, create a REMOTE.BAT file: A:>COPY CON: REMOTE.BAT TMODEM 1, 1200, P ^Z <RETURN> Having created the two "batch" files, we can now invoke TANDEM by simply typing HOST at the operating system prompt on the host computer. And, we can invoke TMODEM by typing REMOTE on the remote computer. On the diskette you are going to be using on the host computer, it is suggested that one additional "batch" file be added. Create an AUTOEXEC.BAT file as follows: A:>COPY CON: AUTOEXEC.BAT SET COMSPEC=d:\path\COMMAND.COM HOST ^Z <RETURN> Note: "d:" is the disk drive specification, usually "A:" and "\path\" is the directory where COMMAND.COM will always be available. FAILURE TO PROVIDE A PATH TO COMMAND.COM WILL CAUSE TANDEM TO MALFUNCTION! Refer to your operating system manual for more information on the SET COMSPEC command. The diskette with the AUTOEXEC.BAT file should be used to boot the TANDEM host computer system. It should be left in the boot drive at all times, especially when the host system is left unattended and there is a chance of a power failure. TANDEM does not, normally, write on this diskette, therefore, it can be protected with a "protect tab." If you wish, you may add additional commands to the AUTOEXEC.BAT file. For example, you may wish to use one or more of the popular memory resident programs. Memory resident programs should be loaded before TANDEM, therefore, they should be inserted in the AUTOEXEC.BAT file prior to the TANDEM command line. 6 PASSWORDS Passwords are used to protect the TANDEM system from unauthorized intrusion. The PASSWRDS.DAT file must be present when TANDEM is started. It contains a list of, up to ten, passwords that are composed of any printable ASCII characters, one password per line. All of the following examples are valid passwords: John JOHN JOHN SMITH 1345-X-ROBERT When you sign on the system, passwords must be entered exactly as they appear in the PASSWRDS.DAT file. Capital letters must be entered as capital letters, lower case letters must be entered in lower case. Note that John, JOHN and JOHN SMITH are three different passwords and will not be confused by TANDEM. The space between JOHN and SMITH is considered to be a part of the password. The PASSWRDS.DAT file can be created using the operating system COPY command, or your favorite ASCII text editor. WordStar document files are not acceptable and will not work. A sample PASSWRDS.DAT file is included on your distribution diskette as an example; it should be replaced with a list of passwords you invent. The password system works like this: When you call the host system, after contact is established between the two computers, the host computer will request that you enter a password. PASSWORD: _ Enter one of the passwords from the PASSWRDS.DAT file, followed by a RETURN (or ENTER). If you make a mistake (typing error), the system will respond with "TRY AGAIN". You have three shots at getting it correct, then you're out! After the third attempt, TANDEM will simply hang up the phone. This should prevent unauthorized persons from just trying random words to get into your system. If no characters are typed for 20-seconds, TANDEM will assume no one is there and hang up the phone. 7 OPERATING TANDEM FROM A "REMOTE" LOCATION First boot the host computer system using the diskette with the AUTOEXEC.BAT and HOST.BAT files (see GETTING STARTED), or, if you prefer, just type TANDEM at the operating system prompt; you will then be asked to furnish the missing parameters - COM port, baud rate, etc. The TANDEM program will initialize the system and then display the selected configuration for a few seconds. The monitor screen will then clear, even the cursor will not be visible. If you are going to leave the host system unattended and your monitor has a power switch, you may turn the monitor off. If you have booted the system with a floppy diskette, we suggest you leave this diskette in the drive. If you replace it with another diskette, the replacement must have a copy of COMMAND.COM on it, or you must provide the operating system with a path to COMMAND.COM, otherwise, TANDEM will not function correctly. At the remote location, boot the remote computer and run the REMOTE command (see GETTING STARTED). Or, you may just type TMODEM at the operating system prompt; you will then be asked to furnish the missing parameters - COM port, baud rate, etc. The remote modem program will then ask you to enter the phone number to be dialed. The number you enter will be sent to the modem exactly as you enter it. For example, if you enter: (229) 776-4321, then "(229) 776-4321" will be sent to your modem. Most modems accept the punctuation, check your modem manual to be sure. TMODEM will then wait for your modem to respond with a "CONNECT" message. Sometimes, because of noise on the phone lines, the "CONNECT" message may be garbled. If this happens, press the ESCape key, enter the letter "C" and a RETURN. This will force the TMODEM program to continue as though the proper "CONNECT" message had been received from the modem. Pressing the ESCape key before the modem responds with "CONNECT" will cause the phone to hang up. You may enter another number, or re-dial the same one by entering the letter "R" and a RETURN. To exit from TMODEM without establishing contact with the host computer, you can press the ESCape key 4-times (your computer will "beep"). Once contact has been established with the host computer, TANDEM will ask for a "PASSWORD:", (see the section on PASSWORDS). Enter the correct password and TANDEM will sign on with the "TANDEM:>" prompt. From the TANDEM:> prompt, there are a number of special TANDEM commands you can run. Each of these commands is discussed in the following paragraphs: 8 CLS - Clears the screen and re-displays the TANDEM:> prompt. DIR - Displays the current directory or you may specify a disk drive and path name. For example: TANDEM:>DIR B:\WORK\ would display the directory for disk drive B:, subdirectory \WORK\. TYPE - Displays an ASCII text file on the screen, pausing after each page. You may specify a disk drive and path name, for example: TYPE B:\WORK\MYDATA.TXT This would display the MYDATA.TXT file found on disk drive B:, subdirectory \WORK\. After each page of text is displayed, press the ESCape key to terminate, or any other key to view the next page. DOS - Takes you to the operating system prompt after loading a second copy of COMMAND.COM into memory. A message reminds you to enter the EXIT command at the DOS prompt to return to the TANDEM:> prompt, you must do so to sign off the system or use the TYPE command, etc. At the DOS prompt, you can issue any command and run almost any program. There are, however, a few programs that will not run correctly, or even worse, lock up the system. See the section on PROBLEM PROGRAMS. With the exception of two keys, the remote computer keyboard works just like the host console keyboard. The two exceptions are the BREAK (CONTROL-SCROLL LOCK), and SHIFT-PrintScreen keys. The SHIFT- PrintScreen key will cause the monitor screen to be printed on the "remote" computer's printer, not the "host" computer's printer. The BREAK key has no affect at all. Because of this, programs that require the BREAK key to terminate should not be run from a remote site. When you are through with the DOS system, always return to the TANDEM:> prompt and issue a BYE or SHUTDOWN command. BYE - Causes TANDEM to hang up the phone and recycle to await the next caller. DO NOT FAIL TO RUN THE "BYE" COMMAND (or SHUTDOWN command, see below). If you terminate the remote modem program without giving the BYE command, your computer is left wide open to anyone who comes along. They won't even need a password! The BYE command will cause the remote modem program to terminate. SHUTDOWN - This command allows you to terminate TANDEM on the host computer from a remote location. TANDEM will ask; "Are you sure ?", if you answer with a "Y" for yes, TANDEM will close down. ONCE A "SHUTDOWN" COMMAND HAS BEEN EXECUTED, TANDEM CAN ONLY BE RESTARTED FROM THE "HOST" COMPUTER. This command should only be given when you are certain that no further calls will be made to the "host" computer. Normally, either the BYE or SHUTDOWN commands will cause the TMODEM program to exit to the operating system prompt. If, for some reason, it is necessary to exit TMODEM without issuing BYE or SHUTDOWN, then hold down the ESCape key (or press it at least eight times), the computer will beep several times before exiting.... 9 EXTENDED COMMANDS The extended commands (LDIR, LDOS, CHAT, and SEND) are available only with the extended version of the TANDEM Remote System. The extended version can be identified by the letter "E" appended to the revision number (e.g. Rev. 3.0E). The following paragraphs discuss the operation of the extended commands: LDIR - The LDIR command displays a directory of the remote computer system disks, similar to the DIR command discussed above. As with the DIR command, you may specify a disk drive and path name. Note that this directory information is not displayed on the host computer console. LDOS - Similar to the DOS command, the LDOS command allows you to access the remote computer's operating system - without loosing the phone connection. A message reminds you not to forget to return and sign off the system when you are finished. You return by typing EXIT at the operating system prompt. The LDOS command can be used to change directories, erase files, rename files, etc. The information being displayed on the remote computer's screen will not be displayed on the host computer's screen. CHAT - Switches you to the CHAT MODE and provides a clear screen so that you can communicate with someone at the host console without prompts, beeps, and other things getting in your way. You can ring the bell (beep) on the host computer by typing CONTROL-G (press the "G" key while holding down the CONTROL key). Similarly, the CONTROL-L key can be used to clear the screen. You exit the CHAT MODE by hitting the ESCape key. SEND - The SEND command is used to transfer files between the "host" and "remote" computers. The SEND command line is constructed as follows: TANDEM:>SEND direction d:\path\FILENAME.EXT [d:\path\FILENAME.EXT] The "direction" parameter uses the symbol ">" to indicate "to," or the symbol "<" to indicate "from." One of these two symbols coupled with the word "Host" or "Remote" establishes the direction in which the specified file is to be transmitted. If you wish, the words "Host" and "Remote" can be abbreviated to "H" and "R". Therefore: >HOST indicates that the source file (see below) is to be sent from the "remote" computer to the "host computer. <REMOTE means exactly the same thing as ">HOST". >REMOTE indicates that the source file is to be sent from the "host" computer to the "remote" computer. Just the opposite of the above two direction indicators. <HOST means exactly the same thing as ">REMOTE". The next parameter is the "source" file name. A disk drive letter and path name are optional, the file name and extension are required. If no drive letter or path name is given, then the source file is assumed to 10 be on the currently logged disk drive and directory. The last parameter is optional; this is the "destination" file name. A disk drive letter and path name are optional. If the destination file name is not specified, it is assumed to be identical with source file name, including disk drive letter and path name. Note: A file name must be included with a disk drive letter and/or path name. Excepting the added "direction" parameter, the SEND command works very much like the operating system COPY command. For example, to send a file called "MYSTUFF.DAT" on drive "B:" subdirectory "\WORK\" on the remote computer to the host computer's drive "C:" subdirectory "\TEXT\" with the file name "YOURSTUF.DAT", you would enter the following: TANDEM:>SEND >HOST B:\WORK\MYSTUFF.DAT C:\TEXT\YOURSTUF.DAT If the transfer is to take place using the currently logged disk drives on both computers, and the source and destination files are to have the same names, all you need to enter would be the following: TANDEM:>SEND >HOST MYSTUFF.DAT This would cause the file named "MYSTUFF.DAT" to be transmitted to the host computer, creating a copy of the original file from the remote computer. If the destination file name is that of an existing file, TANDEM will ask if you wish to erase the file. Answer with a "Y" (for Yes) to erase the existing file, or "N" (for No) to return to the TANDEM prompt. The ability to erase (over write) and existing file on the remote computer is not permitted when the SEND command is issued from the host console. While transmitting the specified file from one computer to the other, the following status information is displayed on both the host and remote screens: transfer direction, source file name, destination file name, the number of 128-byte blocks to be sent, the number of blocks transmitted, the number of repeated transmissions required because of errors in transmission, the starting time, and upon completion, the ending time. After the file transfer is completed, aborted, or terminated due to a problem that makes it impossible to continue, a final status message is displayed. Normally, this will be FILE TRANSFERRED. Press the ESCape key to return to the TANDEM prompt immediately. If you do nothing, return to the TANDEM prompt is automatic after a few seconds. During transmission of a file, the transfer can be aborted by pressing the ESCape key. Appropriate messages will be displayed on the "End Status" message line. The time it takes to transfer a file from one computer to the other varies due to a number of factors; the serial port/modem speed, the quality of the transmission lines, and even the computer's operating speed. However, at 1200-baud, it takes slightly longer than one-second to transmit one 128-byte block of data. At 300-baud it takes four times 11 as long. Therefore, to transfer an 128,000-byte file, with your serial port/modem running at 1200-baud, would take over 1,000-seconds or about 17-minutes. FROM THE "HOST" CONSOLE After starting TANDEM and the screen clears, you may still operate the host computer from the host console. You do this by typing "LOCAL" and a RETURN on the host keyboard. TANDEM will, as it does for a remote call, ask for a PASSWORD:. Enter a valid password and TANDEM will display the TANDEM:> prompt. Operation is just as though you had called in from a remote location. For calls to be accepted, you must sign off using the BYE command. The host computer keyboard is always active, even when a remote user is operating the system. This feature allows two people to run a program "in tandem." FROM A "REMOTE" TERMINAL TANDEM can be operated using a remote H/Z-19 terminal instead of another computer running TMODEM. Note, the system must be started using the command line "H" option. Operation is essentially the same, except that the terminal will only display the first 24-lines of data showing on the host monitor. Also, since the terminal keyboard does not have the ALTernate key, we have substituted combination of ESCape, CONTROL-{A thru Z} to serve as ALTernate-{A thru Z}. Even so, many programs cannot be controlled from an H/Z-19 terminal because it has only eight function keys and lacksther necessary features. WHEN TWO COMPUTER ARE CONNECTED BY CABLE Two computers can be directly connected by an RS-232C null modem cable (see the section on EQUIPMENT). Since no modems are involved, dialing the phone is not possible, in fact, meaningless. However, password checking is still in force. Otherwise, TANDEM operates exactly as it does through a modem and the phone lines. You may, of course, use one of the higher baud rates. Running at 2400-baud works very nicely, 9600- baud is even better; however, some computers are incapable of supporting 9600-baud --- try it to determine if any problems exist. 12 PROBLEM PROGRAMS Most application programs will run under TANDEM. However, there are some exceptions, generally problem programs that fall into one or more of the following categories: 1. Programs that use the same COM port that TANDEM is using, such as another modem program. It is okay for a program to use one of the COM ports, so long as it is not the one TANDEM is using. 2. Programs that assume direct (and absolute) control over the keyboard. Few programs do this. The QuickBASIC compiler editor is an example of one that does. The result is a locked remote system --- the "host" keyboard still operates, but the "remote" keyboard will not work. 3. Programs that use dot graphics. TANDEM does not support dot graphics (character graphics are okay). Running one of these programs causes strange things to happen to the remote screen. Returning to the operating system prompt clears the problem. 4. Programs that use animation may not work very well. This is due to the relatively slow transmission of data from the host to the remote. SOME PROGRAMS YOU SHOULD NOT RUN: The QuickBASIC compiler's editor (Microsoft, Inc) SideKick (Borland Int) SOME PROGRAMS THAT HAVE BEEN TESTED (and run okay): Microsoft's assembler, MASM (Microsoft, Inc) GW-BASIC (Microsoft, Inc) Turbo Pascal (Borland Int) GALAXY (OmniVerse) PC-WRITE (Quicksoft, Inc) Right Hand Man (RHM) (Red E Products, Inc) POPALARM (Bell Soft, Inc) SDIR (Public Domain) PROCOMM (Datastorm Technologies, Inc) Z80MU (Z-80 emulator) (Computerwise Consulting Services) Utah FORTRAN (Ellis Computing, Inc) FORMAT, COPY, TREE, and other DOS commands. Let us know what programs you have ran successfully and we will expand this listing. 13 IN CASE OF DIFFICULTY If you have a problem with TANDEM, we suggest the following points to check: 1. Check the equipment. Could be someone unplugged the RS-232C cable or something like that. 2. Is your modem on the COM port you think it is? Have you selected the proper baud rate? 3. Recycle your equipment. Some modems will hang up for no apparent reason, turning them off and on will clear things. 4. Is the printer turned off? Trying to print with it off will sometimes hang the system. 5. Are there diskettes in all disk drives and the doors closed? Some systems will hang if you try to access a drive that can't run. 6. From the remote system, it may appear at times that TANDEM does some strange things with the display screen. This usually happens during scrolling of the screen or when menus pop-up. Be patient and things will eventually settle down. 7. If someone picks up a phone on the modem line, the resultant noise may cause the screen to blow up! Exit the program you are running and issue a CLS command. 8. If you should get an error message from TANDEM itself, we don't think it can happen, then TANDEM will do its best to lock the system. This has been done to prevent unauthorized access to your computer. 9. If your problem is none of the above, take a few moments and drop us a line. Tell us what you were doing and what happened. We'll do our best to help you solve the problem. 14 USER SUPPORT We know that The TANDEM Remote System is not perfect. We will continue to work to improve it, but we also need your help. Your suggestions steer us in the right direction and even help to squash those nasty "bugs." If you have a suggestion or a problem, let us hear from you. Write to the following address: Louis E. Wheeler P.O. Box 888 Oceano, CA 93445 15