C/C++ Users Group Library 1996 July

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User Manual for YAM (Yet Another Modem) by Chuck Forsberg (Converted for MS-DOS and Lattice-C) by Olen Pederson 1. Highlights Conversational mode with optional capture to file and multiple page review of past output. File capture of long files works with any system which responds to XON-XOFF protocol. Flexible uploading of suitable files to many types of remote systems, even Bulletin Boards without normal uploading capability. Error checking file exchange with programs using Ward Christensen's protocol with optional Cyclic Redundancy Check. Enhanced error recovery and transfer abort logic. Batch transmission of files with compatible programs. High speed operation, 9600 baud file transfer and conversational terminal operation. Buffered printer operation at >>1200 baud. Full printer buffering allows use of slow printers, or printers with burst transfers (line printer, MX80, etc.). Function key escape sequences can be buffered, allowing proper operation when keyboard baudrate exceeds host baud rate. Disk utility functions including directory listing, change disk and/or directory, erase files, disk free space calculation, file transfer time calculation, CRCK file check, and local listing of files. Full support for pathnames, subdirectorys. Great flexibility in specifying filenames. New data may be appended to existing ASCII files. Optionally, YAM can maintain log of files sent and/or received with disk, filename, baud rate, and the name of the remote system. Written in C, a modern high level systems language for ease of portability and maintenance. 2. Definitions CAPTURE When in the T(term) function, ALL data coming from the remote is captured in a circular buffer. DUMPING When a receive file is open as a result of a "t filename" command, and the circular buffer is nearly full, that data is written out to the receive file if Dumping is on. Setting Squelch mode (see below) turns Dumping off until a ^R character is encountered. FUNCTION An operation supported by yam, such as DIR, TYPE, S, R, or T(term). A command may set or reset a MODE, or perform 0 or more FUNCTIONS. HOST The ``other machine'' with which YAM is communicating. This may be with either a direct RS-232 connection or through a pair of modems. MODE Many modes affect the way the term function handles data. OPTION Option(s) apply to the S and R commands only. PREFIX A letter that prefixes a command to modify its action. REPLOT Traditional term (from early days of Tek Graphics) referring to the rapid redisplay of previously calculated information. In the case of YAM, the data remaining in the capture buffer may be paged and/or searched with the replot function. {} Required argument. [] Optional argument. pattern ... An empty pattern represents all files on the default disk in the current working directory. A disk identifier without filename represents all files on that disk in the current directory. Unambiguous and ambiguous filenames may be specified in any combination. A pattern may contain any combination of the above. 3. Prefixes and Commands 3.1 a: Change to a: disk (or b, etc.) some versions print the free disk space in kilobytes. 3.2 b m Set baudrate to m. Example: "b 9200" 3.3 br{eak} Sends a break. 3.4 bye Dump any connection in progress by dropping DTR (data terminal ready). A call or on command must be given to reassert DTR before making or answering another data call. 3.5 call name If the first character of name is a letter, yam searches the PHONES file for name. If the search is successful, enable Data Terminal Ready (DTR), and set baudrate to the value (if present) corresponding to name. If autodial is supported, dial the telephone number. The specifics of autodial operation may vary with the implementation. If autodial is notsupported, the telephone number is displayed. It is not necessary to type the entire name as it appears in the file, as YAM will find the first entry that is a prefix of name. If the first character of name is not a letter, yam assumes a telephone number has been entered directly. Example: "call tcbbs" or "call tc" 3.6 cd pattern ... change current directory to pathname. Function the same as the dos or Unix cd command. 3.7 ch change port configuration. System will prompt for data bits, parity and stop bits. 3.8 chat Chat keyboard to keyboard. Characters typed by either keyboard are echoed to both ends, and RETURNS echo as RETURN/LINEFEED. Chat will become hostile if the other end also echoes characters. 3.9 close Dump capture buffer if a receive file is open, close files. 3.10 crc [pattern ...] Print the "crc" checksum and character count for the specified files. The checksum is calculated with the same alogrithim as the CP/M CHEK.COM program. This command is slower but possibly more accurate than the crck command. 3.11 crck [pattern ...] Print the "crck" checksum and sector count for the specified files. The "crck" algorithm is stolen from version 4.3 CRCK.ASM. 3.12 e{mode[s]} Enable mode(s) affecting file transmission/reception with the term function. (The "s" and "r" commands always send data transparently.) 3.13 d{mode[s]} Disable mode(s) affecting file transmission/reception with the term function. 3.14 debug Cause an interrupt to the operating system for use with debuggers. The MS-DOS version does an INT 3. NOTE: the debugger must have previously set up the vector location for this command to function properly. 3.15 del pattern ... Delete the named files. For each matched pathname, the user is prompted for Y, N, or Q. Y erases the file, N skips to the next file, and Q or anything else aborts the command. 3.16 dir [pattern ...] Displays the directory with the number of bytes in each file. The number of files matched, number of blocks, number of kb allocated to those files, and estimated transmission time at the current baudrate for all files listed are displayed. Transmission time estimate is based on batch transmission and the formula: blocks per minute = (Baudrate*60)/(10 bits each char * 136 chars) Time does not include error correction. The usual ambiguous filenames are allowed. Example: "dir" "dir *.c" "dir yam*.c" "dir *.c *.h" 3.17 dump [pattern ...] Dump the named files in side by side hex/ascii format. Zero length files will not be displayed. 3.18 f[mode[s]] name Send file 'name' in the term function. The optional mode enables one or modes. If squelch is enabled, preface with ^R and append with ^T. 3.19 help Displays a command summary. This command closes any open send file. 3.20 init{ialize} Initializes yam to all its default values. Does not reset the modem or file system(see "reset"). 3.21 kill Kill all data in the capture buffer. Restores the pointers to their initial positions. 3.22 mn Change data port to (decimal) n. Example: "m1" The domain of correct port numbers and consequences arising from incorrect port numbers vary with the implementation. 3.23 o{ff} Disable the modem by turning off DTR. 3.24 pxm Set Parameter x to value m. 3.25 pwd Print pathname to the current working directory. 3.26 qu quit to DOS without dropping DTR to modem. This allows exit to the operating system, and subsequent re-entry without causing the modem to disconnect. 3.27 reset [size] Dump the capture buffer; if a file is open, close all files, and reset modem. The optional argument size becomes the size of the circular capture buffer, useful for debugging. 3.38 replot [m] Redisplay the last m lines and/or escape sequences received from the host. If m is 0 or absent, redisplay starting with the earliest data. A screenful is displayed at a time. The commands accepted in replot mode are listed below. 3.39 rewind Rewind the buffer pointers for the display, printer, and file dump from the term function. The effect of this command is the same as if the data had been sent another time. 3.40 r[options] [file ...] Receive with options 1 or more files using the Ward Christensen protocol. If no filename is given, batch mode is assumed. (Note: batch mode is not compatible with MODEM7). If more than one filename is given, a single file transfer will be made for each. If the RESTRICTED option is defined, a file received in error will be unlinked (erased). 3.41 s Displays status information about YAM configuration. 3.42 sum pattern ... Sums the named source files with an algorithm compatible with sum(1) on Version 7 Unix (sum -r on System III). Carriage returns, and all characters starting with CPMEOF are excluded from the calculation. This processing allows comparison of source files stored on different systems but not ``binary'' files. 3.43 s[options] pattern ... If batch mode is specified with the b option, 0 or more files are sent according to the ambiguous pathname(s). If batch mode is not specified, the named unambiguous file(s) are sent each in single file mode. 3.44 tab n Set tab expansion to n. If n=0, or not present, the tabs are reset to the default as found in the configuration file. 3.45 type pattern [...] Type the file(s) specified by one or more possibly ambiguous pattern(s). This command closes any open send file. Yam compiled with USQ defined will automatically detect squeezed files and print them in ASCII. Type stops/resumes printing with ^S. Keyboarding ^C cancels, and ^X skips to the next file. 3.46 t[c][mode] [file] The term function with optional capture to file. 0 or more modes may be enabled. The c (close) mode causes data in the capture buffer to be written to file and closed immediately. View mode causes the term function to display control characters by prefixing ^ to the corresponding letter. Characters with the 8th bit set will be prefixed by a ~. If the free buffer space becomes low, yam attempts an xoff-dump-xon sequence. A receive file previously opened by 't file' will not be closed by a 't'command. Keyboarded characters are treated in either of two ways depending on the value of Exitchar (see parameters, below). If Exitchar is non zero, term will return when a character matching Exitchar is keyboarded, and all others are passed without any special action. Otherwise, the following subcommands are available: 3.46.1 ^b Break. Sends a break signal to the remote. The break key on your terminal will probably generate a ^@ (NULL) character. After the break is sent, any remaining keyboard input (usually garbage from a break character) is discarded. 3.46.2 ^E Exits from the term function back to main command level. Rapidly typing ^E^E will instead cause one ^E to be transmitted. 3.46.4 ^Q If a send file is open and its transmission has been stopped by a XOFF, transmission is resumed. Otherwise no special treatment. 3.47.4 ^S If a send file is open and it is being transmitted, transmission is stopped. Otherwise no special treatment. 3.46.6 ^R Replots up to 24 lines starting with either the first character received after the last character keyboarded, or as much as in the buffer if less than 24 lines have been received. This allows the output from the last command to be conveniently reviewed. Replot then awaits next replot command (see below). ^R^R typed quickly sends one ^R instead. The following received characters are recognized in the term function, when they are fetched from the circular buffer for the display. 3.46.8 SO If Cis02 mode is in effect, turns on the Compuserve A protocol. This protocol is used with the XFTRAN program and the DOW command of SIG/ACCESS. See yam4.c and Compuserve's CP-MIG user group for more information. 3.46.9 XOFF Stops file transmission from yam. 3.46.10 XON Resumes file transmission. 3.46.11 TAB Some versions of YAM expand tab characters to spaces on the display. BUG: Since YAM does not decode cursor addressing commands, these commands should not be intermixed with tabs on the same line. 3.47 w Write dumps the circular buffer to the receive file, if open. 3.48 wc pattern ... Takes a count of lines, words, characters excluding returns, and all text characters for the given files. Characters beginning with CPMEOF are excluded. On 8 many versions, counts are modulo 64k. 3.49 x same as bye. 3.50 ! command Create a shell to execute a DOS command. For this function to work, the dos PATH must be set so the file command.com can be found. For Lattice-C versions, SWITCHAR must be not be reset from the default "\". 3.51 ; Semicolon is an optional command delimiter which may be used in place of RETURN in order to place multiple commands on a line. 4. MODES used with D, E, F, T or U commands ! Negates the sense of the following mode. For example, t!l will turn off the line printer. 2 Enables Compuserve A protocol if this feature is included. N.B. Non-ASCII files or files without CR's must be uploaded in Cpmpuserve's binary mode. a A return from the keyboard is sent as return, linefeed. If half duplex, both are sent to the console. b Binary mode of TRANSMISSION with T function. All 8 bits are sent. Handy for downloading binary files to adjacent machines without any modem program. Don't confuse this with the S function which uses the Christensen protocol. Also don't confuse with i mode which affects files received with the T function. d Directly enables/disables dumping of captured text is squelch mode is in effect. If squelch mode is not in effect, always enables dumping. e with term command, echo characters received from the host to the host. Use this only for keyboard to keyboard communication, and then only at one end. Reset after each command. Does not imply "Half Duplex". With the f command, selects an alternate file transmission function sendecho() which waits for an echo to each character transmitted (for Throttle/10 seconds). The echoed character is output to console. See "propagating yam" below. Often it is fairly easy to write a simple receive routine which synchronizes with the sender by the simple expedient of echoing the characters received. On Heath/Zenith CP/M system, the pip device "TTY:" does just that. f Full duplex. g Resumes (GO) sending file once in the term function, equivalent to XON. Disabling GO causes a file queued for transmission to wait for an XON character. h Half Duplex. Displays keyboarded characters as they are sent to the host. i Ignrx flag. When set this will cause characters defined by the RXNONO string to be ignored in the term() mode. If reset, all characterts are passed thru. This flag may be set or reset by the call command based on information in YAMPHONE.T. k Set the buffer size used in the s or r commmands. Non-compatible with MODEM7. l List unit (Printer) on. Since the printer is separately buffered, it needn't be as fast as the incoming data as long as the difference doesn't exceed the buffer size. The rewind command may be used to get extra copies of the received data. n Called nlmode, after the corresponding tty mode in Unix systems. Send NEWLINE (lf) only when transmitting file (no CR). Send keyboarded CR as NEWLINE. When receiving a file to disk with the term function, NEWLINE is stored on disk as \\r \\n. p When sending files with the term command, wait to receive GOchar after sending a CR at the end of a line. The default for GOchar is linefeed (see parameter g below). If GOchar is not received, the wait times out and transmission proceeds in the same manner as with w mode. The duration of this timeout is controlled by the p parameter. r Called crmode. Sends CR only at the end of each transmitted line. s Squelch the dumping of captured data with ^T and unsquelch with ^R. These characters are not copied to the file. When a receive file is opened with Squelch mode is selected, writing to the file is turned off. Selecting squelch mode automatically turns writing off; disabling squelch automatically turns it on. (See "d" above). t If Waitnum is more than 1, wait for echoes to stop after sending each Waitnum characters for period Pause. If Waitnum==1, send at 1/Throttle, measured in loops of the term() function. The default values of Waitnum and Throttle provide transmission at about 50 words per minute regardless of baud rate. This is handy because many remote systems cannot accept input at full speed. v View control characters as ^C. Useful in shutting up the bloody bell. In addition to the above, v distinguishes characters with the parity bit set by prepending a tilde (~). Note: View mode is distinct from view option. This mode is reset after each command. w When sending files with the term command, send CR only at end of line, and then pause until echoes from remote have stopped. Useful for sending files to bulletin boards where the remote needs time to prepare for the next text line. The length of this pause is controlled by the p parameter. x exit from the term function when EOF is encountered on transmitted file. z Close file when ^Z is encountered while dumping the capture buffer. Otherwise ^Z is ignored. It should be noted that ``The Source'' coughs up an occasional ^Z just as the "UPI" program is about to output something interesting. 5. Options used with S and R commands All options are reset after each command. b Batch option. In receive, filenames are provided by the sender. Pathname(s) may be specified as a batch option for file reception(i.e rb /usr/cat/). Filenames provided by the sender will be appended to the specified path name. Disk and subdirectory names are excluded from the transmitted pathname(s). c Request Cyclic Redundancy Check instead of simple checksum. This option must be specified with the R function. The receiving program automatically signals the sending program if CRC is to be used. The probability of an undetected transmission error is much less if CRC is used in place of arithmetic checksum. k Use 1 K byte blocks with the S and R functions. Default block length is 128. Increases throughput when the baudrate is high, relative to the response times of the channel and computers. The k option may not work properly on all systems, especially at high baud rates. q Quiet option inhibits some of the status information. Unlike some other programs, quiet option is not necessary for proper file file transfer at higher baudrates. t Execute the term function after file transfer(s) complete. v View the data being transmitted. Correct data is displayed once. Viewing ascii files does not interfere with correct transmission at extreme baud rates, although throughput will be affected. For each sector, data is viewed once before sending/after receiving. y Yes it is OK to clobber a file already on disk. If absent, the operator is given a choice of appending to the current file (a), erasing it (y) or aborting (n). 6. Parameters used with P command gm Set GOchar to m (decimal). Default is linefeed. (See p mode.) Some remote systems accept uploads with a ? for each line. Optimum operation with such a system might call for pg63 pp10000 pt90 ftw filename. The first sets the go ahead character to question mark, the second sets the timeout to a long delay, the third sets throttle to a speed which allows the remote to echo at 300 baud (assuming no tabs), and finally the command to send the file with throttle and wait at end of line (also eliminating the lf). If this sounds too complex you can always go back to longhand. em Set Exitchar to m (decimal). Same format as GOchar discussed above. If defined (non-zero), term function will return when m is keyboarded, and ALL other keyboarded characters are passed to the remote. If special function keys have been defined for replot and exit they will still be recognized. Otherwise, be sure not to set Exitchar to something you can't keyboard! wn Set Waitnum to n. See "w" mode for details. Default is 1. tm Set Throttle to m. The default value corresponds to about 80 words per minute sending speed. pm Set Pause to m. When the free characters in the circular buffer reach LOWATER, an XOFF is sent. Pause controls the time which must then pass without characters received before believing that the other end really has obeyed the XOFF character, as opposed to the sometimes lengthy Compuserve hitches in the getalong. If Pause is too short, it is possible that a lurch in output will be interpreted as acknowledgement of the XOFF, only to have more characters arrive whilst yam is occupied dumping the buffer to disk. When this happens, unfortunate characters are routed to the proverbial bit bucket, and you can retry the download as the timesharing service increments the connect charge. The default value seems suitable for Source over Tymnet and BBS systems. Pause is also the echo wait period used with the w mode, as well as the timeout for p mode. Some bulletin board programs require a very long pause when accepting files with the p or w mode. 7. Replot Commands Commands within replot consist of a single character. Replot maps uppercase, lowercase, and control characters together in decoding commands. b Display beginning of buffer. k Kill entire buffer contents and return. r,BS Display previous page (some overlap is provided). SP Display the next page. / Accept a search string, terminated by return. Search through the buffer starting at the current location for the first (next) instance of that string (matches either case). Display page starts with that line. If the search is unsuccessful, ring bell and jump to the beginning of the buffer. n Search for next occurrence of the previously entered search string. p Backup one line and redisplay. LF Advance one line. x Exit after displaying the last page of buffer contents. This restores the screen and keyboard to the same state they were in before replot was entered. X allows you to see where you were if you were in the midst of keyboarding a command to the remote. For example, suppose you are typing in a line of commands and you need to "thumb back" through the remote's output for some vital nugget of information. (After you enter a 20 line email message, NOW Compuserve asks you for the 8 digit account number to mail it to!) So you hit some Control V's until you see it on the screen. Now you can't remember whether you typed a space after the last part of you command to the remote. No sweat, just exit replot with x and you'll see just where you were (But don't forget that number!) X may not redisplay the entire page contents if the host has been sending escape sequences in the last page. 8. Special files There are 3 special files used with YAM. Actual file names are defined in YAMSYS.H with the defaults being "YAMCFG.T", "YAMHELP.T" and "YAMPHONE.T". YAM will search all directorys in the default search path to find these files. The data from the first sucessful pathname search is used. YAMCFG.T This file is the startup configuration file. It contains the signon prompt, initial serial port definition, definition of the RXNONO string, xon-xoff parameters, and others depending on the implementation. YAMHELP.T This file contains a summary of commands and is displayed by the "h[elp]" command. YAMPHONE.T This is the phone list file used by the CALL command. Call searches each line of this file until it finds a match. It then configures the modem port as defined by the parameters following the phone number. The phone number must be delimted by a <TAB> character. Modem baud rate is defined by a lower case 'b' followed by a number. Several letters following the baud rate define the number of stop bits(S1, S2), parity none, even or odd(PN,PE,PO), and the number of data bits(D7,D8). The flags field define optional flags which may be turned on. At the time of this writing only the Igrnx flag is defined. This will set or reset the i flag as defined in the "ei" command. 9. Sample YAM Session A sample session on MS-DOS might be: C>YAM invoke yam b 9200;b: Set 9.6 kb, Change to b disk dir yam*.* List files and calculate xmsn time sb yam*.* Send them to a system supporting the YAM batch mode call hydepark Call the number found in phonelist user data Enter a message, etc. ^E exit from term mode ftp letter Open 'letter' and send to bbs, using prompt and throttle modes to slow transmission so the remote system won't drop characters. YAM remains in T(erm) after the file is sent. xmodem s foo.bqr Command host to download a file ^E rt secret.tqp Download the file using MODEM7 protocol, then back to term function dir command to list directory on remote system ^R pause ^R Flip back two pages to first part of directory listed previously CR Back to term function user data More keyboarding with remote, logoff ^E exit (if CDO defined, term will exit by itself) bye Drop DTR so modem won't answer calls, Return to DOS 10. Notes When operating with a timesharing system and/or through network or satellite links, considerable delays in transmission and responce to blocks may severely reduce throughput of an FTP (file transfer protocol). The k option causes the s command to use 1024 byte blocks, rather than the standard 128. At high baud rates, this reduces the protocol related overhead up to 87 per cent, depending on file length, by reducing the number of blocks which must be sent and acknowledged by a factor of 8. 1024 byte blocks are selected by the sender. An STX at the beginning of each block (otherwise SOH for 128 bytes) indicates this block is 1k long. Pathnames are always sent with 128 byte blocks. Buffering problems on some timesharing systems may mitigate against use of 1k blocks at high baudrates. Files transmitted from Unix to CP/M will be padded with ^Z characters as necessary to reach a length divisable by 128. CP/M files sent with 1k blocks may not compare identically with their originals due to the addition of up to seven extra 128 byte sectors (padded with CPMEOF). Readiness to receive sectors with Cyclic Redundancy Check (2 bytes) instead of the usual additive checksum is indicated by a 0103 (ASCII "C") for initial "naks" instead of 025. CRC option is highly recommended. It is the default when using batch mode and/or 1k blocks. File transmission is compatible with MODEM7 in single file, standard block length mode. File transmission may be aborted by sending a SEQUENCE of CAN (^X) characters. Each character keyboarded will cause readline() to return a TIMEOUT error, thus regaining keyboard control relatively easily. Maximum baudrate possible without errors using the t(erm) function depends on the computer and particular yam implementation, but usually is 9600 baud. Use these numbers for comparison. Your mileage and range may differ depending on clock speed, circuit distance and RFI/EMI. California estimate lower. Quiet mode is not necessary for proper operation at 19kb, although it does increase throughput slightly. View option (S and R commands) does not decrease maximum baud rate, although throughput is obviously affected according to the ratio of terminal speed to communications rate. Printer operation with bios calls or view mode substantially reduces the highest baudrate possible with the term function without losing characters (independent of actual printer speed). The term function will send XOFF to prevent buffer overflow if the printer is on, or if a receive file is in use. In the term function, use of the circular buffer provides some advantages. Incoming data may come in at a rate higher than the display and/or printer. Tab expansion for the display does not compromise this ability. The user may decide to save a timesharing session on the disk AFTER it has started (or possibly even finished) as long as the buffer pointers have not wrapped around. The same ability also applies to the printer. The printer need not be as fast as the host as long as the Tortoise is allowed to catch up. Received data may be redisplayed (replot command). At high speeds, the display will fall behind the incoming data, as storing of raw host data into the buffer takes precedence over all else. As a result, a defective or incorrectly programmed port which sources data at high speed can lockout the keyboard. If yam "goes away" when entering the term function, this may be the cause. The t and z modes affecting dumping of captured data take effect when the circular buffer is written to the receive file, not as the characters are first received from the data port. The append option (available if receiving filename where filename exists) operates by by utilizing the append option of the C open command. 11. Downloading Files from Unix(TM) Systems To download files from Unix systems with sb, invoke sb(1) to send the desired files and then use the yam ``r[yt]'' command. On Unix type: sb file ... Then exit term with ^E and give ry and file transfers will commence. If the files are long, and/or if the baudrate is limited, you can save time by squeezing them first with sq(1). Versions of the BDS C programs SQ, TYPE, and USQ are available for Unix systems. The CP/M version of USQ supports a -n option which will expand Unix NL's to CR/LF. The Unix version -n flag suppresses carriage returns. If a file or set of files are to be transported between Unix systems with yam, it is helpful to place them in a tar(1) archive (and possibly squeeze the archive) before transmission. This procedure will preserve the modification times and avoid adding ^Z characters to the ends of files. The -k option of sb will select 1 kb block length rather than the standard 128 bytes for improved throughput at high baudrates. Currently this does not work at 9600 baud with the Z100 under MSB. Consult the sb.1 manual entry for more information. 12. Uploading Files to Unix(TM) Systems On Unix systems, files may be uploaded with rb(1). See the rb.1 manual entry for more information. 13. Error Correcting File Transfer with Other(UGH) Remote Systems If the host system has YAM, XYAM, MODEM, XMODEM, tmodem, umodem, or something compatible, you can upload files with the s command on your computer and the corresponding r command on the remote. Newer versions of some of these programs support Cyclic Redundancy Check as an alternative to the simple checksum used by the original Ward Christensen protocol. CRC is much better at detecting errors and I recommend its use where available. Unfortunately, this protocol is not implemented on the popular timesharing services The Source and Compuserve. It is often possible to upload files using the F command, perhaps with one or more modes. Your chances of success improve if you set "enab flow" when connecting to Telenet. If using Tymnet, type ^R^X just before the host computer name to enable flow control with XOFF and XON. It often helps to use "half duplex" when connecting to the computer. Yam4 implements the Compuserve `A' protocol which is usable only on Compuserve's own network. The determined hacker will divine alternative ways to transfer files by a close examination of the rest of this document. 14. BUGS Yam does not trap any escape sequences from the computer which can lock up the keyboard or display. If yam appears to be locked up, check the terminal by itself to see if perhaps it is wedged. Not all commands are implemented on all versions. When YAM is used with a terminal (or terminal emulation) which accepts commands to transmit information to the host (screen dump, cursor position, indent, etc.), the characters so generated may cause YAM to do strange things. The most common manifestation of this is in replot mode, where the automatically generated characters may cause YAM to exit replot. Yam gets its input in term() mode from low level bios functions. This was done for speed but has the side effect of disableing many keyboard re-definition utilities. readbaud() must return a valid #. Otherwise baudrate will be 0 and routines which use it(especially dir) will fail with a divide by 0 error. sb *.* will report an error when it encounters a subdirectory. It recovers and the error message can be ignored. rb pathname may send a pathname NAK to the other system before it is ready, depending on the speed of the host. This is especially true when using a ram disk to receive files. break on control-c may not be recognized properly if DOS BREAK ON is set.