IBM PC X-talk.
Version 1.01 A. Howitt Sept. 1984.
Introduction :
The IBM PC X-talk program is a communications package using asynchronous
protocols to provide a utility for transferring files to and from the
Edinburgh Multi-Access System (EMAS) via a Terminal Control Processor
(TCP). The program was written originally for the Sirius computer by
Robin E. Day of Business Studies and hence the user interface is
similar on both machines.
In order to run the program DOS Version 2.00 operating system must be
used with the extended screen and keyboard control device driver. This
can be accomplished by placing the command :
DEVICE=ANSI.SYS
in your CONFIG.SYS (configuration) file. (See DOS manual Chap. 9 & 13.)
After rebooting the system it will be possible to establish
communication with EMAS but before files can be transfered two OPTION
settings will be required in your EMAS process.
1). Insert file MICROS.EMASLIB.
2). Set interactive terminal input buffer size to 16 Kbytes.
This is achieved by the following sequence in response to the EMAS
prompt :
Command:OPTION(SEARCHDIR=MICROS.EMASLIB)
Command:OPTION(ITINSIZE=16)
The program is available to EMAS/IBM PC users from the ERCC Service
Support Group, as an external command file (.EXE), but the user must
supply his own disks. The default arrangement is for communications on
COM1 port, parallel printer port LPT1, and a communications rate of 2400
Baud. Facilities exist within the program to temporarily reset the
options for particular sessions.
Program Overview :
The program provides several facilities, the principal one being to
enable the IBM PC to operate as an EMAS terminal. EMAS files may be
listed to a parallel printer attached to the IBM PC , if desired,
without being retained on the IBM PC storage system. The program also
permits the transmission of files between EMAS and the IBM PC disks, in
either direction.
The cable connection between the serial port of the IBM PC and the EMAS
TCP must be approved (and can be supplied) by the ERCC Service Support
Group.
Setting Up The Communications Link :
1. Connect serial output port COM1 to the TCP port by means of an ERCC
approved cable.
2. Boot the IBM PC DOS Version 2.00 operating system.
3. Load a disk containing the external command module XTALK.EXE and
give the instruction:
XTALK
4. The program will clear the screen and display a heading, then wait
for user action.
5. If it is desired to operate the system with a baud rate different to
the default option, then type ^B to enter the temporary
installation stage. (Hold down the Ctrl key, and press B at the
same time).
6. If it is desired to establish network connection, press the space
bar in the normal EMAS terminal log-on manner.
7. It is now possible to use EMAS or any other computer on the network.
Information passing between the IBM PC user and the remote host, is
buffered by the XTALK program before display on the IBM PC screen. If a
parallel printer is attached to the IBM PC, then the information
appearing on the screen may be 'slaved' to the printer. This may be
achieved by typing ^P on the IBM PC, at the point printing is to
commence. Printing may be terminated by a further ^P which will switch
off printing immediately, but since most modern printers have a buffer
printing may continue until drained. Because printers are normally
slower than communication rates, it is possible to exceed the buffer
capacity of XTALK (5K), if long printng outputs are requested. The user
should limit this printing mode to small output requests and should
wait, if possible, for the printer to catch up. For larger outputs the
user should study the list facility provided by the XTALK program, where
no such limitations apply.
Temporary Installation Changes :
It was explained earlier that there is a default arrangement for the
serial port baud rate. This will normally be customised for a
particular user when first obtaining the program. It is realised
however, that situations may arise when a variation of this arrangement
may be desired. The program provides for such eventualities and may be
requested from the 'terminal emulation' mode of operation. This should
normally be carried out prior to network attachement.
Installation phase may be entered by typing ^B (holding down the Ctrl
key, and pressing B at the same time).
The program will respond with :
S(et baud rate), Q(uit):
Pressing the single letter Q will exit the user from the installation
phase, back to 'terminal emulation' mode, and the user may then log-on
to the network in the normal way. Any changes made during the
installation phase will be effected when exit from the phase takes
place.
Pressing the single letter S will cause the program to respond with a
prompt for Baud rate selection.
Baud rate: A(300), B(600), C(1200), D(2400):
The user should select the desired baud-rate by typing the relevant
single letter reference. Although the prompt only indictaed baud rates
up to 2400, which is the normal EMAS limit, the program will accept
letters E and F for rates of 4800 and 9600 respectively.
Transfer Of Files :
It is sometimes desired that EMAS files be available on the IBM PC, or
IBM PC files be available on EMAS. A link mode for bulk transfer of
files may be established from the terminal emulation mode by typing ^L
(hold down the Ctrl key and press L at the same time). The program will
respond with the link mode menu.
G(et), P(ut), L(ist), Q(uit link), B(inary), C(haracter), E(xit):
Any of these facilities are effected by typing the relevant single
letter reference.
During the transfer of files, the information being transferred is not
displayed but an asterisk is flashed on the screen whilst transfer is
taking place.
E(xit)
The letter E will exit from link-mode back to the terminal emulation
state, and EMAS will trigger the Command: prompt.
Q(uit link)
The letter Q will send the stop command to the remote host, to log-off,
and exit from the XTALK program back to DOS. The user may log-off in
the terminal emulation mode by typing STOP or QUIT in the normal way.
If, however, it is desired to return to DOS, then it is still necessary
to type ^L Q. If STOP is typed in the terminal emulation mode, then the
user may log-on to another process or computer on the network, in the
normal way, by pressing the space bar to start the procedure.
B(inary), C(haracter)
XTALK allows for files to be transferred in binary or in character mode.
The need for alternatives is becuase EMAS does not store the 'return'
character in character files. It is therefore necessary to either
remove or insert a return character, depending on the direction of
transfer, whenever a 'line-feed' is encountered. The removal and
insertion of characters in true binary file transfer would, of course,be
disasterous. C(haracter) type transfers are assumed by default.
G(et)
The letter G indicates that a file is to be transferred from EMAS to a
disk on the IBM PC .
XTALK will first request the name of the EMAS file which it is desired
to transfer. This should be typed followed by a 'return' character.
The program will then request the name of the EMAS file which it is
desired to transfer. This should be typed followed by a 'return'
character. The program will then reqeust the IBM PC filename, which
should be given, preceded by the drive identifier (if not the currently
selected) and include an extension, if desired.
e.g.
EMAS filename: ABCD
IBM PC filename: B:SABCD.DAT
Neither list of filenames must exceed the line length.
P(ut)
The letter P indicates that a file is to be transferred from the IBM PC
to EMAS. The specification of filenames to be transferred is identical
to that explained for G(et) above.
L(ist)
The letter L indicates that an EMAS file is to be printed (listed), on
the printer attached to the IBM PC parallel port. Transfer is very
similar to that described under G(et), except that only EMAS filenames
are requested. The limitation on the quantity to be printed , which was
indicated earlier, does not apply when the L(ist) operation is
requested. There is no limit on the quantity to be printed.
Information transferred under L(ist) and printed is not retained on the
IBM PC or on its disks.
N.B. Since the information to be printed is buffered into the IBM PC,
printing will not take place until either the transfer buffer is
full or the total file of information has been received.
The program will not be able to cope with the following situations :
a. Insufficient storage or index space on either system.
b. Communication or computer failures.
c. Operator messages from EMAS during transfer.
(While transfer takes place all messages are suppressed)
If there is a link breakdown, for any reason, between the IBM PC and
EMAS while transfer is taking place, then the XTALK program may be left
in a 'hang-up' state. In some circumstances the hang-up may be broken
by typing a question mark (?), which is the terminator for bulk transfer
to EMAS. On other occasions it may be necessary to re-boot DOS and
re-enter XTALK. Control may then usually be regained by typing a
'return' or ESC A 'return'. If all efforts to recovery fail and the
EMAS process is still running such that it is not possible to get back
to Command level, then the last resort is to telephone the computer
operator and ask for the process to be discontinued. The need for this
drastic action should be rare.