IMP (NOTES ON HOW TO USE) Copyright 1985 Irvin M. Hoff W6FFC 01 OCT 1985 INTRODUCTION: ------------ NOTE: THIS PROGRAM SUPPORTS ANY 1200 OR 2400 BPS MODEM INTENDED FOR AUTO- DIALING WITH THE "AT" PROTOCOL OR THE RACAL-VADIC PROTOCOL. IT ALSO SUPPORTS THE PROMETHEUS PROMODEM EXTENDED-"AT" 1200 BPS PROTOCOL. NOTE: IMP v241 adds KMD-type batch protocol in addi- tion to the MODEM7 type. It comes up in KMD batch. Use the command TBM to toggle batch mode to MODEM7 type if needed. RCPM systems with KMD/BYE500 support the KMD-type batch mode. The IMP modem program enables a computer to communicate with another computer. This is normally done by using standard telephone lines but with special audio tones sending serial data. Three common speeds are used, depending on the facilities available -- 300, 1200 or 2400 bps. ('bps' stands for bits per second. One character is 10 bits per second, normally. It may be 11 bits if two stop pulses are used.) WHAT IS A MODEM? --------------- A "modem" is used which provides these audio tones. This is an acronym for "modulator and demodulator". The one section (modulator) provides the audio tones for sending over the telephone line and the other section (demodulator) then converts those audio tones back to dig- ital pulses the computer uses to receive the incoming data. The modem itself is a hardware utility, usually costing around $75 to $200 for a typical 300 Baud device and from $200 to $450 for a system offering 1200 Baud as well as 300 Baud. The newest modems add 2400 bps and currently can be obtained from $435 to "way on up". (The so-called "list prices" are rarely paid even with single-unit purchases.) Some modems are intended for plugging directly into the computer while a vast majority are external devices that connect to the computer through a serial I/O connector. These are often designed to sit under the phone itself to minimize space required. An external modem has sev- eral advantages as most have numerous indicator lamps telling the user what is happening. This also makes it far more simple to use the modem on any of several computers the user may have. AUTO-STEPDOWN, A NEW MODEM FEATURE -------------------------------- The newer 300/1200/2400 bps intelligent modems have the ability to determine the maximum speed (baudrate) at which the system they are calling can use. They adjust themselves accordingly, without operator intervention or knowledge. They send a "result code" back to the local computer telling it what speed they now have. This information can be used to automatically set the local computer to the same speed. A mes- sage is displayed telling the operator what speed he has. If the operator has a reason for using less than the maximum speed to which another system might respond, he can initially restrict the modem from attempting to connect at a faster speed. Example, Compu- serve has modems that will answer at either 1200 or 300 bps. If reading and answering messages "on line in real time" many callers prefer to use 300 baud (they cannot type even that fast) rather than 1200 bps which is nearly twice the cost. IMP takes advantage of this automatic stepdown feature. It has the modem attempt to connect at 2400 bps. If that is unavailable at the answering end, the modem tries for 1200 bps. When connected, IMP shows the speed currently in use and automatically adjusts the local I/O to match. (IMP is the first and currently the only free modem program to take advantage of this new modem feature.) The operator can easily select the "SET" command should he wish to override the automatic "start trying at 2400" and have a specific speed dialed (such as 300 baud for Compuserve for hand typing messages at lower cost, etc.) The automatic feature is reinstated by either using the "SET" command for 2400, or merely calling up the modem program from the disk once more. Note: The US Robotics Courier auto-steps from 2400 to 1200 but not to 300, as do most of the other new modems with 2400 bps. PURPOSE ------- The program discussed in this guide allows each computer involved to directly control its own modem, converting DC pulses into audio tones which are sent to (or received from) the telephone line. (The standard 1200 baud transmissions use "DPSK" (dibit phase shift keying) instead of "AFSK" (audio frequency shift keying). For short distances, no modems are required as the computer can provide the necessary digital voltages. This discussion is centered around systems intended for use over distances ranging from several miles to literally around the world. FEATURES: -------- A program to communicate with another computer can range from very simple to very complex. Although IMP has a number of quite useful fea- tures (some of which other modem programs do not currently offer) it is one of the easier programs to learn and use. A list of some of the features offered by this particular program include: 1) Ability to talk with another computer via keyboard at each end. (Called the "terminal mode".) 2) Ability to operate a remote mainframe computer such as TYM-SHAR, or special data bank systems now commonplace. This includes "bulletin board" systems for receiving, sending or just read- ing messges or other types of information. 3) Ability to upload (send) or download (receive) programs from other computers whether TYM-SHAR, data banks, remote hobby systems or just another individual in another location. 4) Ability to automatically transfer a group of files (called "batch mode". Two popular methods included, KMD batch mode and the older MODEM7 batch mode. 5) Ability to copy incoming information on a printer. If the print- er is too slow to copy the data directly, the extra characters back into a large storage buffer until they can be printed. 6) Ability to copy incoming data into memory for automatic transfer to a disk file. 7) Accomodates any computer clock speed up to 25.5 MHz. in 0.1 Mhz. increments for uniform results. (The clock speed is actually of modest interest, it is only used for setting timing loops.) 8) Advanced type of error detection (CRC or Cyclic Redundancy Check) using automatically generated high-speed lookup tables. 9) Ability to send any of 10 different pre-programmed function keys. (These keys are very easy to reset, using either of two exter- programs provided.) 10) Automatic disconnect from the telephone line when using CTL-N, "D" or "Z" as an option during file transfer. 11) Automatic or manual 1k protocol for increased throughput and effi- ciency over the 128 character blocks long associated with such programs. 12) Supports 1200 or 2400 bps modems using the Racal-Vadic or 'AT' protocol developed by Hayes. These features basically include automatic dialing and redialing until the system being called finally answers. a) Automatic selection of a particular phone number from a library of names and numbers. (These phone numbers can be very easily changed by using either of two ex- ternal programs that are provided.) b) Automatic dialing for alternate long-distance systems (where auto-dialing touch-tone modems are used). c) Entry of a hand-typed number. Although it might be as simple to manually dial the number as hand-type it, it can then be automatically redialed indefinitely. d) Auto-linking of 1-32 different numbers for continuous dialing until one of the group is available. e) Choice of beeping continuously when connected to get the operator's attention, or beep one time and go to terminal mode immediately to catch UNIX or IBM signon messages that assume you can copy when connected. f) Automatically adjusts the terminal speed to that of system answering the phone. USING THE PROGRAM THE FIRST TIME: -------------------------------- For now, we shall assume the program is ready to use on your equip- ment. (Normally the user must make some modest changes to the program before it can be used. This includes changing the port numbers and some other personal options. These will be covered later in the section that describes how to adapt it to your equipment.) When the program is brought up is shows this display (if using the PMMI modem): IMP v240 modem pgm (type M for Menu) Copyright (c) 1985 Irvin M. Hoff Version for Datapoint 1560 modem port 28H Modem speed is: 2400 bps B>>COMMAND: x (Your version would have a different line 3 once the ap- propriate overlay was added and the baudrate might show show 1200 if you do not have 2400 available.) The cursor stops at point "x:" waiting for some sort of command. Typing a "M" followed immediately by a RETURN, shows the first page of a 3-page help guide. Several commands are similar to those already used for CP/M, such as 'ERA', 'DIR' and the ability to change disk drives and user areas. This adds tremendous flexibility while remaining in the modem command mode. To change disk drives, just say: B>>COMMAND: A: <cr> and you are in the same user area on the A: drive. You can also say: A>>COMMAND: A12: <cr> to change user areas. When finished (using this example), say: A12>>COMMAND: CPM <cr> or A12>>COMMAND: BYE <cr> and you will go back to CP/M with the original drive and user area. OPTIONS: ------- There are 6 primary options and 9 secondary options that may be typed on the command line. In addition there are over numerous commands ranging from single character to three charac...
Amiga7878