Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 9, NO. 5 / MAY 1983 / PAGE 43

Modem80. (evaluation) Robert Jacobs.


Modem80 is a package of communications software for the TRS-80 which is easy to use and sufficiently flexible for all normal computer communications. With this program one may successfully access bulletin boards, other TRS-80s, mainframe computers which permit telephone access, and other brands of micro-computers. Files may be transferred to and from other computers provided they can be set up either to receive ASCII files or to operate under the protocol of the CP/M program Modem.

Files may be sent in their entirety or a line at a time--as for example, to get material into a mainframe text editor such as SOS or TECO. The Modem80 package--which consists of seven separate programs--is extraordinarily versatile.


The main program of the package is MODEM80/CMD. Like the other offerings on the disk it may be copied without difficulty and runs perfectly under TRSDOS, NEWDOS 2.1, NEWDOS-80 (both versions), DOSPLUS, and LDOS. Modem80/CMD loads, initializes the RS-232 parameters, and then presents the user with a menu which lists a variety of activities. By using simple control codes (the CLEAR key is designated as a control switch), you can set the system up to receive or send a disk file, toggle the printer on or off, or transmit some of the characters left off the TRS-80 keyboard. Alternatively, you may switch to the main menu, which offers additional possibilities.

All file transfers are to or from disk; a large buffer is established to which or from which file material is sent. During the transmission, you may query the system and receive a report of file and buffer status. One advantage of this procedure is that files of unlimited length may be sent or received--or, more precisely, the largest files your disk storage system will handle may be received and sent.

Transmission may be interrupted at any time, and it is even possible to break certain kinds of files in the middle and put the remainder on a different disk. Another advantage of a disk-oriented system is that files may be prepared off-line, by programs such as Scripsit, and saved to disk. Then, should there be some transmission difficulty, the material is still safely ensconced on your disk, ready for another try.

Disk file material may be intermixed with keyboard characters, thus permitting the transmission of data to computers that cannot accept full-speed transmission and which do not use control codes to start and stop the transmission.

Reception of files is nearly as flexible, especially if the sending computer can be set up to respond to control codes, since under MODEM80/CMD the TRS-80 can be set up to use any ASCII control code needed to regulate the sending machine. Control codes may also be used to permit the remote computer to control the file operations.

Two file transmission protocols are available. The first is a handshaking protocol compatible with the widely used CP/M program Modem. As files are transmitted, they are checksummed in blocks, and the checksums verified at either end. Should a block be transmitted incorrectly, Modem80 automatically retransmits it. Any type of file may be transmitted or received, whether TRS-80 compatible or not. This protocol requires that the remote computer be using a similar program. Should this condition not exist, transmission and reception of files may still take place--but here you are limited to ASCII files. You may send or receive text or Basic programs saved in ASCII under the A option, or a binary file may be converted to an ASCII file by using the utility HEX/CMD, supplied with the Modem80 package. Thus the limitation to ASCII files turns out not to be a limitation; in fact, HEX/CMD offers a file checksum also, so that you may verify correct reception by comparing the sent version to the received version. And naturally, an ASCII file may be converted back to binary form by the final option offered under HEX/CMD.

The main menu of MODEM/CMD permits a good deal of local housekeeping. The user selects between "echo' and "terminal' modes so that full-duplex transmission may take place between computers (one of the two should be on "echo'). All of the RS-232 functions may be altered from the keyboard by changing local communication parameters. In addition, you can set the system for full or half-duplex, to add linefeeds to carriage returns, to send nulls after carriage returns, to receive graphics, and to print line feeds or not. In short, complete flexibility is offered, and though my description of the program may make it appear complex, it is, in fact, easy to use.

Other Programs

The remaining programs are also interesting. HOST1/CMD allows remote control of the computer, and XMODEM/CMD is a file transfer utility which may be run under HOST1 so as to permit file transfers under the control of the remote computer. Only in this case must both computers be using Modem80 or other derivative of CP/M.

TYPE/CMD, also included as part of the package, lists a file on the display or printer and may be used under HOST1 to send a file to a remote computer or terminal. TYPE/CMD responds to the XON-XOFF protocol used by so many mainframe computers and thus fulfills a function that XMODEM does not.

The last two programs, SAVE/CMD and TEXTFIX/CMD, assist in the preparation of disk files for transmission. SAVE/CMD allows one to key directly to disk, thus permitting off-line text file preparation. If the user does not have a word processing program available, this utility fills the gap. TEXTFIX cleans up text files by removing control chearacters so that the received file may be loaded into a word processor. It also has the ability to add the terminal zeroes required by Visicalc and Electric Pencil files. These are not the kinds to things one uses often, but when you do need them, you need them badly.


I have been using this package for several purposes. The simplest has been to transfer materials back and forth from friends' TRS-80s and from Model I to III, for which it is ideal. I also access bulletin boards and Micronet occasionally and with complete success.

The most demanding application has been contact with my university's computers--a DEC-10 and a VAX. The flexibility of the Modem80 package has allowed me to transfer text, Basic, and Fortran files without difficulty.

The author of Modem80, Leslie Mikesell, has done a wonderful job on the documentation, and it is clear that a great deal of thought has gone into the design of the program as well. I was most impressed by Mikesell's provision of four translation tables, which permit alteration of all the control codes, establishment of special keys, redefinition of transmitted or display characters and the like. These are the output, video, disk, and printer translation tables. All are readily alterable by the user by entering DEBUG, and although most applications will not require such changes, some will. The ability to make these changes is an important attribute of smart terminal programs.

This package of programs is an excellent value. It will serve the communications needs of practically every user. In several months of heavy use, I have yet to discover a bug in it and have had no difficulty with either specialized or common applications.

Products: The Alternate Source Modem80(Modem) - Evaluation