%OP%TNT
%OP%BON
%OP%PL64
%OP%AMM
%OP%DPF
%OP%TM1
%OP%HM2
%OP%FM2
%OP%BM1
%OP%LM05
%OP%HE/%H2%Z88 Users' Club Software Library%H2%/
%OP%FO/Z185/@P@//
%CO:A,12,70%
%R%%H2%SXX%H2% Shubunkinsoft XModem Transfer
%R%by Tom Hawkins and Phil Wheeler

%R%Instructions


%H2%SXX%H2% is an XModem file transfer package intended as a simpler 
alternative to a "Link" package such as PC-Link, for transferring 
files between the Z88 and a desktop computer.  Because the standard 
XModem protocol is used, the desktop machine only needs to run a 
communications package (as found in many integrated software packages 
such as MS Works) and it is not necessary to load the special Link 
software.  This is an advantage for Z88 users who don't own a desktop 
PC but have to "borrow" one to do their file backups, as it 
eliminates the risk of spreading viruses on the software disc.  With 
%H2%SXX%H2% any make and model of computer can be used for backups, whatever 
the floppy disc format etc., provided it has an XModem package and an 
appropriate connecting cable.  It's also free!

The user interface and backup generation code for %H2%SXX%H2% was written by 
Tom Hawkins (4666).  The code for performing the XModem transfer is 
taken from %H2%Z88COM%H2% by Phil Wheeler, which is available from the 
Software Library as Z051.


%H2%How to use SXX%H2%

Before starting %H2%SXX%H2%, go to the Panel with []S and set the appropriate 
receive and transmit rates.  Set 'Parity' to None and 'Xon/Xoff' to 
%H2%No%H2% as %H2%SXX%H2% performs its own handshaking during the transfer.

Start %H2%SXX%H2% by CHAINing it, or LOADing it and typing RUN.  
"Assembling..." is displayed while the machine code is assembled, 
then the menu is displayed with the following options:

Receive 
Send
Send Group of files
Set last-backup date


To choose an option, use the up and down keys then ENTER, or press 
the appropriate letter.  To exit from the program, press ESC.


%H2%Receive%H2%

On choosing 'Receive' you are asked for the filename of the file to 
be received.  Tell the sending computer to start sending, then type 
the filename and press ENTER on the Z88.  It isn't critical whether 
the sender or receiver is started first, as they will synchronise 
within a few seconds.  Once the transfer starts, its progress and the 
number of 128-byte blocks received is displayed in the bottom half of 
the screen.  If nothing happens within 15 seconds, %H2%SXX%H2% will abandon 
the transfer.

If the transfer is successful, %H2%SXX%H2% will return to the menu.  
Otherwise, an error message is displayed and you are prompted to 
press a key to continue.



%H2%Send%H2%

On choosing 'Send' you are asked for the filename of the file to be 
sent.  Type the filename and press ENTER, then tell the receiving 
computer to receive.  As before, it may be a few seconds before the 
transfer starts.  The length of the file in 128-byte blocks is 
displayed.  Messages in the lower half of the screen describe the 
progress of the transfer.  If nothing happens for 15 seconds, %H2%SXX%H2% 
will abandon the transfer.

If the transfer is successful, %H2%SXX%H2% will return to the menu.  
Otherwise, an error message is displayed and you are prompted to 
press a key to continue.

If the file you specified could not be found, or couldn't be opened 
due to an error such as 'In use', %H2%SXX%H2% will beep and display the 
message "Can't open the file", then ask you for the filename again.

After a file has been successfully sent, the date, time and filename 
are appended to a file called %H4%xfiles.log%H4%.  This forms a record of 
which files have been transferred and when.  It can be examined and 
printed by loading it into Pipedream with the 'Load as plain text' 
option set to Yes.  %H4%xfiles.log%H4% can be erased if it is not required.  
The full filename is specified by the variable lgf$, which is defined 
close to the beginning of the program.  To change the name of the 
file, or to specify a different device and directory, change the 
program line which defines lgf$ and SAVE the program again.

%H4%Note:%H4% Avoid pressing ESC during the send or receive operation as this 
may leave files open, producing the 'In use' error when you later try 
to access the file.  The only way to cure this error is a soft reset.  
If there is a problem with the transfer, such as the other computer 
failing to respond, %H2%SXX%H2% will abort after 15 seconds of inactivity.  
Additionally, %H2%SXX%H2% is unable to detect when a send has been terminated 
by pressing ESC and will log the filename to %H4%xfiles.log%H4% as though it 
had been successfully transferred.


%H2%Send group of files%H2%

This option provides a means of backing-up files from the Z88 to a 
desktop computer.

On choosing 'Send group of files', you are asked for a "file 
specification".  This should be a filename containing wildcards so as 
to specify all the files you want to send.  For example, %H4%/letters//*%H4% 
would specify all the files in the %H4%letters%H4% directory and its 
subdirectories.  %H2%SXX%H2% then prompts, "Send only files updated since:" 
and gives the date of the last backup.  To accept this date, press 
ENTER; to specify a different date, use the editing keys to change 
it, keeping the format (eg) "12-Jun-1992 09:30:27", then press ENTER; 
to send all files irrespective of date, delete the line with <>D then 
press ENTER.

%H2%SXX%H2% now uses a CLI routine to generate a list of the files you 
specified.  If there are a lot of files, this may take some time.  
%H2%SXX%H2% then displays "Searching" and goes through the list looking for 
files updated since the specified date.  On finding one, it prompts: 
"Send %H4%(filename)%H4%?".  To send the file, press ENTER.  To miss it out 
and move on to the next file in the list, press N then ENTER.  When 
the end of the list is reached, %H2%SXX%H2% returns to the menu.

%H4%Note 1:%H4% The date given at the "Send only files updated since" prompt 
is stored in a file called %H4%sxxlast.dat%H4%.  If this file is missing, no 
date will be given at the prompt.  To create the file, use the 'Set 
last-backup date' option (see below).  

%H4%Note 2:%H4%  No error checking is done on the "Send only files updated 
since" date in this version of %H2%SXX%H2%!  Type carefully!

%H4%Note 3:%H4%  To generate the list of files to send, %H2%SXX%H2% uses the []+S CLI 
sequence to create a file called %H4%s.sgn%H4% in the :RAM.- device.  This 
file is erased at the end of the 'Send group of files' operation.  It 
is not recommended to give a "File specification" which includes 
:RAM.- as this may cause an error.  For example, if you want to back 
up all files on RAM, don't type %H4%:RAM.?//*%H4% but do a separate 'Send 
group of files' for each RAM device.  If a file called %H4%s.sgn%H4% is 
present in :RAM.- when %H2%SXX%H2% is started, it will be erased.  If %H2%SXX%H2% is 
interrupted, eg by pressing ESC, while in the middle of a 'Send group 
of files' operation, the %H4%s.sgn%H4% file will be left in :RAM.- and should 
be erased using the Filer.


%H2%Set last-backup date%H2%

Choosing 'Set last-backup date' allows the time and date which appear 
at the "Send only files updated since" prompt (see above) to be set.  
You will be prompted with the current time and date; press ENTER to 
accept this or use the editing keys to change it.  (See Note 2 
above.)

The last-backup date is stored in a file called %H4%sxxlast.dat%H4%.  The 
name of this file is specified by a variable called lxf$, which is 
defined close to the beginning of the program.  To give the file a 
different name, or to specify a different device and directory, 
change the program line which defines lxf$ and SAVE the program 
again.


%H2%Exiting from SXX%H2%

To exit from %H2%SXX%H2% press ESC while the menu screen is displayed.  %H2%SXX%H2% 
may also be safely <>KILLed from the Index while in this condition.


%H2%The XModem protocol%H2%

The XModem protocol was written for the public domain by Ward 
Christiensen in 1977 or so and its intimate details should be fairly 
easy to find out if you want to know - try a bulletin board for 
starters.  Essentially, the %H4%sending%H4% computer waits until it receives 
an ASCII NAK character (21) then sends a 128-byte block of data with 
a header identifying its block number and a checksum byte which the 
receiving computer uses to detect errors in transmission.  If the 
receiving computer receives the block correctly, it transmits ACK (6) 
and waits for the next block; if the block was received corrupted, 
the receiver transmits a NAK and the sender retransmits the block.  
An upgraded version of XModem uses a cyclic redundancy check (CRC) 
instead of the checksum to verify that the data is uncorrupted; this 
has much better immunity to errors going undetected.  %H2%SXX%H2% does not 
use the CRC; however, a computer running XModem-CRC will revert to 
the ordinary protocol if the machine on the other end doesn't 
respond.  If your transfers always take a few seconds to get started, 
this is probably what's going on.

%H4%Note:%H4% Because XModem does not transmit the actual length of the file, 
the file as received will contain up to 127 extra characters to make 
its length up to a multiple of 128 bytes.  In the case of a BASIC 
program received by the Z88 these characters can be ignored and will 
be lost next time the program is LOADed then SAVEd.  In the case of a 
Pipedream file the extra characters will appear after the lowest 
occupied slot in the rightmost non-empty column and may be deleted.  
For other files, such as CLIs and PrinterEds, the extra characters 
may cause problems.  Before using such a file after it has been 
loaded into the Z88 via %H2%SXX%H2%, it should be loaded into Pipedream as 
'Plain text', and the extra characters deleted before saving it, 
again as 'Plain text'.

This problem has been addressed in later updates of XModem such as 
YModem and ZModem, which send not only the length but also the 
filename and creation and modification dates of the file.  They also 
allow for sending and receiving batches of files and for using longer 
blocks to speed up transfer where line conditions are good.  I have 
the details of both these protocols...  but for the money for the 
Developer's Notes and the time to write and debug the code I'd 
implement them for the Z88...  if you're interested in doing this 
please get in touch, otherwise don't hold your breath, kids!


%H2%Wiring the connecting cable%H2%

The only connections required between the two computers are: RxD on 
the Z88 to TxD on the other machine, TxD on the Z88 to RxD on the 
other, and GND on the Z88 to GND on the other.  This is known as a 
%H4%null modem%H4% cable.  Additionally, connections must be made between 
some pins in the plug at each end to put the correct voltage on each 
computer's 'handshaking' inputs for data to be sent.

%P0%
Suggested configurations for connecting cables are:




Connect:



Also connect:
(within the plug)

I believe the PC-Link cable should work with %H2%SXX%H2% although I haven't 
tried it myself.  There's only one way of wiring up the BBC port so I 
assume the BBC-Link cable will work.  However (that sounded too 
simple didn't it?) remember there are two ways of inserting the plug 
into the BBC!  Work out which is correct then LABEL which is the top 
of your plug!

These instructions were written by:

Tom Hawkins (4666), 44 Harborough Road, Southampton SO1 2FY

28th April 1992
%CO:B,12,66%%CO:C,12,54%



































R
S
G
D
























































































































































































Z88


2 (TxD) to
3 (RxD) to
7 (GND) to

5 to 8
and 9
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PC/XT
(25-pin)

3
2
7

6 to 8
and 20
%CO:E,12,30%































































































































































































































PC/AT
(9-pin)

2
3
5

1 to 4
and 6
%CO:F,18,18% 































































































































































































































BBC B
(DIN 5C)

A
B
C

D to E
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