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ATS/T\ATS06
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » CEEFAX disks » telesoftware2.adl |
| Filename: | ATS/T\ATS06 |
| Read OK: | ✔ |
| File size: | 6665 bytes |
| Load address: | 0000 |
| Exec address: | FFFFFFFF |
File contents
Interactive programming J.J.Brayshaw 1987
Transmission of computer software via teletext is not quite the simple
process it may at first seem. In practice, many factors have to be
considered in order to broadcast the full range of codes included in
telesoftware files. This module looks at some of the problems, and offers
practical routines for downloading any correctly formatted files from any
teletext channel.
__________________________________________________________________________
Teletext Interactive Porgramming:
Advanced Teletext System. 6
(c) J.J.Brayshaw 1987
Telesoftware files:
Computer software designed for use with an 8-bit computer consists
entirely of codes in the range &00 to &FF, or 0 to 255. Transmission of
software via CEEFAX is, therefore, theoretically easy. Just replace the
characters that make up a displayable page with the codes, in the correct
sequence, from a computer program.
Unfortunately, there are a lot of problems in doing this. The CEEFAX
system, as with any teletext system, is designed to work in 7-bit mode.
This means that only 128 of the required 256 codes can be broadcast. The
8th (top) bit of each 8-bit sequence is used for a parity check.
The parity check is necessary not just to check the integrity of the
received data, but also to check and correct the receiver's internal clock
from which it determines when each bit starts and ends. Using "odd parity"
ensures that there is a change of state from zero to one or vice versa (at
individual bit level) in every single code. The clock is designed to reset
itself each time a change of state occurs. In this way, it only needs to
be accurate enough to receive a single byte before a reset is made.
This means that only the lower 7 bits of each code received form the data.
The top bit is either set or clear, whichever will ensure an odd quantity
of bits set in the whole 8-bit byte. The theory is that a decoder should
count the number of bits that are set to one in each byte received. If
this is an even quantity, the byte is in error and the decoder can take
appropriate action. In practice, however, there is little remedial action
a decoder can take when a "parity error" occurs, and consequently this
check is often not carried out. Odd parity transmission is still useful,
however, to ensure clock timing accuracy.
Page 1
Interactive programming J.J.Brayshaw 1987
So teletext transmissions are limited to a maximum of 128 different codes.
This quantity is further reduced by CEEFAX protocols which make it
difficult to broadcast certain codes without adverse effects. For example,
character code 13 will tell a teletext set that double-height text
follows. In this case, the following row should not be broadcast, as it
will be exactly the same as the preceding row and therefore can be
generated by the teletext set, thus saving transmission time. This ensures
a correct double-height display on a CEEFAX page, but will cause severe
problems in a telesoftware file, as one of the packets in the transmitted
sequence will be missing. Some other codes also cause problems at the
transmission or reception stage, and are best avoided.
In order to cater for the broadcast of these untransmittable codes, a
protocol for telesoftware transmissions had to be devised. This was agreed
at the appropriate International Standards committee several years ago,
and has not been changed in any way since. All the telesoftware broadcast
by the BBC since the start of public transmissions in 1983 has been in
accordance with this protocol.
Known as RTF (Redefinable Telesoftware Format), the protocol allows any
one of the 256 possible codes to be transmitted. The file is split into
teletext packets (or rows) for transmission. These are given the standard
CEEFAX protocol which includes a magazine address, a row address, and
odd-parity coding. The decoder must sort the packets into correct order,
then strip the row and magazine addresses from the incoming data. The
length of the page has been extended by two rows to allow for a full 1k of
data to be sent with each CEEFAX page. The telesoftware file can occupy
the centre 24 bytes of packet zero, plus 40 bytes from each of packets 1
to 25 inclusive. This gives 1024 character positions, which is exactly 1k
of data.
The data received is queued in an input buffer. Each byte is taken in turn
and decoded using a 'look-up' table. These look-up tables apply to every
single byte received, and so what appears in the input stream is not
necessarily what is sent to the output file.
Each byte is looked up in one of two tables, and can decode to a single
byte, a string of bytes, or a command. In the first instance, the single
decoded byte is sent to the output file. In the second case a single input
byte can decode to a string of bytes (up to 256 of them!), and each one is
sent to the output file. In this way, a single transmitted byte can
represent several bytes of the final file. In the third instance, a
predefined routine can be engaged to perform any one of a variety of
tasks. This does not necessarily result in anything at all being sent to
the output file!
Page 2
Interactive programming J.J.Brayshaw 1987
The two different look-up tables are known as the 'lone' table and the
'escaped' table. Each byte is looked up in the lone table unless the
decoder is told otherwise.
The RTF protocol assumes the incoming data is in normal 8-bit mode. As we
have seen, the data sent by CEEFAX is generally in 7-bit form. So the
first part of most telesoftware files is a "|" followed by a "B". The "|"
character (double vertical bar in MODE 7) decodes to an instruction. This
instruction tells the decoder to use the 'escaped' decoding table instead
of the 'lone' table for the next byte only. In this case, the next byte is
"B" (&C2) which decodes (in the escaped table) to another command - to
change the contents of the look-up table to a predefined decoding pattern
for 7-bit data. So a "|B" in the input stream tells the decoder the file
is formatted in 7-bit mode, and decoding should take place accordingly.
So, generally, any byte in the input stream immediately following a "|"
symbol is interpreted using the 'escaped' table, otherwise the 'lone'
table is used.
The RTF protocol allows us to change the entries in either decoding table.
The command to do this is sent with the transmitted file. Codes "q", "r",
"s" and "t" in the escaped table tell the decoder to reset the meaning of
a particular code in one of the two tables. For example, the sequence:
|sZ8New text
will reset the entry for "Z" in the lone table to be "New text".
Interpreting each byte in the above line:
| tells the decoder to look up the next byte in the escaped table
s in the escaped table decodes to a command to reset the meaning of the
next byte to be the following string
Z is the character whose entry is to be redefined
8 is how long the new definition string is to be
N } The eight
e } bytes that
w } form the
" " } new definition
t } of the
e } character "Z"
x } in the "lone"
t } decoding table
Following this command, every time the character "Z" is received in the
input stream, the string "New text" will be sent to the output file.
Page 3
Interactive programming J.J.Brayshaw 1987
Most of the entries in the Lone decoding table will decode to 7-bit
versions of themselves. For example, if a code &C1 is received (character
"A"), the lone decoding table will redefine this as code &41 (the 7-bit
version of &C1) which is also character "A" (provided that this entry has
not previously been redefined within the file). However, some codes are
set to decode to commands - in particular, code &60 (underscore character)
decodes to the "raise next byte" command. In this case, the following byte
is received, stripped of parity then added to 88. The result is sent to
the output file. Similarly, code &7E (divide sign or tilde) decodes to the
"lower next byte" command, in which the next byte received is stripped of
parity and reduced by 88. The result (MOD 256) is sent to the output file.
For example, the sequence:
~A
decodes to:
((ASC"A") AND&7F)-88
(ASC"A")=&C1. Strip the parity with "AND &7F" to give &41. Add 88 as
instructed by the ~ character to give &99
In this way, any of the codes 0 to 255 can be transmitted.
The RTF protocols allow for very efficient data compression techniques to
be performed. Using redefinitions wisely has resulted the reduction of the
length of some transmitted files by as much as 50% over the non-compressed
version.
There are, of course, many other features of the RTF protocol, including
the facility for files to be split over more than one CEEFAX page, or to
put more than one file on a single CEEFAX page or sub-page number.
Comments can be included in the formatted text (to be displayed on screen
during the downloading process) and much more.
The RTF protocol is very flexible. Even the commands themselves can be
reallocated to different codes if required.
Page 4
Interactive programming J.J.Brayshaw 1987
The RTF decoding algorithm:
START
|
+----------------+
| |
| +---------------+
| | Get byte |
| +---------------+
| |
| +---------------+
| | Look up the |
| | meaning in the|
| | Lone table |
| +---------------+
| |
| / \ +------+ +----------------+
| /is it\ YES | Get | | look up the |
| <Escape >--------| next |-----| meaning in the |
| \ ? / | byte | | Escaped table |
| \ / +------+ +----------------+
| NO | |
| +----------------------------------+
| |
| / \
| /is it\ YES +---------+
| <Command>--------| Execute |-----------+
| \ ? / | command | |
| \ / +---------+ / \
| NO | / End \ YES
| | < of >-----+
| +--------------+ \block/ |
| | Send byte(s) | \?/ / \
| | to output | | / End \ YES
| | file | NO | <of file>--+
| +--------------+ | \ ? / |
| | | \ / |
| | | NO | STOP
| | | |
| | | +----------+
| | | | Get next |
| | | | block |
| | | +----------+
| | | |
+-----------------+----------------------------------+---------+
Page 5
Interactive programming J.J.Brayshaw 1987
Following the downloading of a telesoftware file, the decoding tables may
have been dynamically altered by the incoming file. Normally, the default
tables should be re-instated before downloading further files. However,
this action can be inhibited if required, allowing a second file to be
decoded using the same decoding tables as set up by the first file. This
could save transmission time and coding if the files require the same
redefinitions to apply. As this is rarely the case, and as it is not
guaranteed that the user will download the files in the correct sequence,
the normal procedure is always to reset the default decoding tables before
any subsequent download. The command "|B", "|C" or "|F" at the start of
the file will reset the tables anyway, regardless of whether they were
reset at the end of the previous file or not.
The decoding of a file through the lone and escaped tables is an entirely
automatic process. All that needs to be done is to tell the ATS which file
to download, and where the file can be found. A few other details about
the file are also required.
All the details for all currently broadcast software are given in a
machine-readable file known as the catalogue file. Before downloading, the
decoder should find and interpret the catalogue information. As it is not
possible to assign a particular page to this catalogue on a permanent
basis, the decoder must be able to discover its location every time
downloading is requested. The catalogue page is pointed to by the 5th link
(link 4) of the teletext service main page (for details of page links, see
module 5). To find the services main (or initial) page, the "initial page"
link of the TSDP must be followed. This is given in the first few bytes of
the TSDP. So, for a telesoftware downloader to operate, it must first
find the TSDP and decode the "initial page" link setting held there. It
then finds this initial page and decodes link 4. Following this link will
lead to the machine-readable catalogue where details of the telesoftware
files can be found.
All the downloaded files are stored in memory, a single CEEFAX pageful at
a time, before being saved to disc. This may require as much as 2k of
workspace (or more) allowing for the expansion of text due to
redefinitions, which ATS allocates at OSHWM. Any downloader written in
BASIC will be immediately corrupted by the incoming file unless PAGE and
OSHWM are separated before starting the downloading procedure. This can be
achieved using a simple OSWORD call as in the accompanying program. The
setting of OSHWM must be returned to normal after downloading.
Page 6
Interactive programming J.J.Brayshaw 1987
The catalogue page is encoded using the same protocols as other
telesoftware (i.e. the RTF protocols). This file is normally downloaded to
computer memory rather than to disc. The file comprises data only, the
first two entries being strings intended for direct display on screen. All
string entries in the catalogue follow the same format: The first byte is
the length of the string - simply read its value directly (with
length%=?(start_of_store%)) - then take the appropriate number of bytes to
form the string. Each byte of the string itself should be OR'ed with &80
before display to counter the effects of parity.
There then follows a quantity of entries, one for each transmitted file,
consisting of eight fields:
Field one is a string giving the computer type for which the file is
intended. For BBC computers, this would be "BBC" or "ANY". A decoder
should only allow files for use with the appropriate computer to be
downloaded. Other files should be ignored.
As each computer must be able to easily identify this information, the
string used has to be clearly defined. Computer types defined so far are:
ANY - For any computer (for example, text files)
AMIGA - Commodore Amiga computers
AMSTRAD - Amstrad computers
ATARIST - Atari ST computers
BBC - BBC Microcomputers (Master, B+ or B)
CBM64 - Commodore 64 computers
CBM128 - Commodore 128 computers
COMM - Acorn Communicators
CPM - Any CPM computer
IBM - IBM computers
MSDOS - Any MSDOS computer
SPECTRUM - Sinclair Spectrum computers
This field is also used to mark the end of the catalogue entries. If this
is found to be "***" then there are no more entries in the catalogue.
Field two is a string, giving the filename. The first byte is a single
colour code character, and is not part of the filename. Adjacent entries
in the catalogue that have the same colour code character describe files
that are to be used in conjunction with each other. A white colour code
character signifies a single file unconnected with any other.
The string in field three specifies the type of file. There are no defined
strings for these, but typical entries here include "Text", "BASIC",
"M/C", "EXEC", "Notes" etc. This can be used as a guide to how to use the
file after downloading.
Page 7
Interactive programming J.J.Brayshaw 1987
Field four is a string giving the size of the file. It is intended for
display only, and no defined format for this information exists. It is
frequently used to describe the quantity of CEEFAX pages occupied by the
file (for example "14 pages"), but may express the size in other forms
such as "1.25k". This should not be used to inform the downloading
software of the total file length. Such information is available within
the coding of the file itself.
The fifth field is the absolute load address of the file. No field length
byte is included as it is always four bytes long. It has the most
significant byte first. There is no interpretation to apply to the byte
values.
Field six is the execution address of the file. As with the load address,
no field length byte is given, it being always four bytes long with the
most significant byte first.
Note that although the catalogue information gives both load and execution
addresses, these are only used to set the correct file attributes when
saving the file. The file will not be stored at the given address during
the downloading procedure. (In some cases, the load address given in the
catalogue is also used to determine the exact position within the output
file to send the decoded block of the file).
The seventh field is a single byte giving the magazine number in which the
file is broadcast.
Field eight is a single byte giving the page number where the start of the
file can be found.
After interpreting the first two strings, the information for each file
appears as in the following example:
Byte of Value Meaning
record of byte
======= ======= =======
Byte 0 &03 Length of the first field of the first file is 3
Byte 1 &40 } The first field string is CHR$(&40 OR &80) +
Byte 2 &CE } CHR$(&CE OR &80) + CHR$(&D9 OR &80) which is "ANY"
Byte 3 &D9 } indicating the file is for any make of computer
Byte 4 &04 The filename is three characters long, with a colour
control code at the beginning
Byte 5 &81 Red colour control code - CHR$(&81 OR &80)
Bytes 6-8 The filename
Byte 9 &04 The file type is four bytes long
Bytes 10-13 The file type
Byte 14 &08 The length of the file is described by the next 8 byte
string
Page 8
Interactive programming J.J.Brayshaw 1987
Bytes 15-22 The file length string
Byte 23 &00 } The absolute load address is &00001900
Byte 24 &00 }
Byte 25 &19 }
Byte 26 &00 }
Byte 27 &00 } The execution address for the file is &00008023
Byte 28 &00 }
Byte 29 &80 }
Byte 30 &23 }
Byte 31 &07 The file is transmitted in magazine 7
Byte 32 &21 The file is transmitted on page 21 of the magazine
The next byte would be the first of the next record.
Once details for each file have been found, the downloading process can
start. It is now a simple matter to ignore any file not required (for
example a file that does not have a computer type of "BBC" or "ANY") or
accept only files with a file type of "TEXT" or "NOTES", etc. It is
important to remember that ATS requires the filename to be in upper-case
letters, even if the filename as decoded from the catalogue contains
lower-case letters. Therefore, each byte in the string fields should be
AND'ed with &5F to ensure it is upper-case, and that it lies in the range
of codes produced by the BBC's keyboard!
The ATS provides a routine to download any file, given certain
information. It must be told the filename (in upper-case, excluding the
preceding colour control code found in the catalogue entry), load address,
execution address, magazine number, page number, whether to load to file
or memory, and whether to reset the RTF decoding tables to their default
settings after downloading.
Using a direct OSWORD call to the ATS allows software to be downloaded
without the need to refer to the catalogue page at all (provided the
necessary details are known about the file in advance). This makes it
possible to download software from any channel, irrespective of whether a
catalogue is being transmitted or not.
By interpreting the catalogue file, automatic downloaders can be created
to cater for any requirements. Download all the files without further
intervention, or download all text-only files, or all those less than 5
pages long, etc. etc. The versatility of this system is endless.
__________________________________________________________________________
Page 9
Interactive programming J.J.Brayshaw 1987
The accompanying program, when run, will download a file from any channel,
and will require the input of the following information:
1. Television channel number
2. Teletext page for the start of the file (the magazine number is
calculated from the given page number)
3. Filename. This MUST be entered in upper case, and otherwise correspond
exactly with that given in the file
4. Absolute load address of the file. If the file contains absolute
addressing within the coding, then the address given here MUST
correspond to the address given in the first block of the file. If the
file addressing within the coded file is a relative address, then the
information given here is only used for setting the file attributes on
saving
5. Execution address of the file (used only for setting the correct file
attributes on saving)
6. File to load to memory or filing system. The downloaded file is
normally saved to disc as each block is received, building up the
complete file on disc. You can, however, opt to download the file into
memory only, if preferred, provided sufficient spare memory is
available!
7. Reset the default tables after downloading. Normally, this should be
done to avoid incorrect decoding of subsequent files. In practice,
however, the tables are usually reset at the start of any subsequent
downloading operation.
To find the load address without reference to the catalogue information,
look at the first page of the telesoftware file. Somewhere towards the
start of the coding should be the command sequence: "|l" or "|m". These
codes indicate the start of the load address data. |l indicates the load
address that follows is an absolute address, and |m shows it is relative
(relative to the begining of the file). There follows a single byte giving
the number of bytes comprising the address. This is in plain ASCII format,
and can be read directly. For example, the coding:
|m41076
shows the address to be a relative one of four bytes long, the address
being &1076. The execution address is not always given in the file itself,
but if it is present it will be preceded by |n for a relative address, or
|o for an absolute address.
Page 10
Interactive programming J.J.Brayshaw 1987
The precise filename can also be found from the first page of a
telesoftware file. Look for a "|a" sequence. This tells the decoder the
filename (and sometimes the version and date) follows.
The command "|a" is followed by a single digit giving the number of fields
(in this case, up to 3). The first field is the filename. The second,
which is optional, is the version number of the file. The third field,
also optional, is the MJD (date) of the file. This is not the transmission
date, but a date connected in some way with the file. For example,
|a34Prog225549024
would mean:
| Use the Escaped table to decode the following byte
a The Escape table decodes this to be "Title, version and Date follows"
3 There are 3 fields to the command
4 The first field is 4 bytes long
P } These four
r } bytes form
o } the file
g } name ("Prog")
2 The second field is 2 bytes long
2 } The second field
5 } (version number) is "25"
5 The third field is 5 bytes long
4 } These 5 bytes
9 } give the
0 } third field
2 } (the Modified
4 } Julian Date) as "49024"
This, therefore, gives the means to download any file from any channel.
Beware, however, as downloading files not intended for the BBC micro may
not be as successful as you might imagine!
Page 11
00000000 0d 0a 0d 0a 0d 0a 0d 0a 49 6e 74 65 72 61 63 74 |........Interact|
00000010 69 76 65 20 70 72 6f 67 72 61 6d 6d 69 6e 67 20 |ive programming |
00000020 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
*
00000040 20 4a 2e 4a 2e 42 72 61 79 73 68 61 77 20 31 39 | J.J.Brayshaw 19|
00000050 38 37 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 54 72 61 6e |87..........Tran|
00000060 73 6d 69 73 73 69 6f 6e 20 6f 66 20 63 6f 6d 70 |smission of comp|
00000070 75 74 65 72 20 73 6f 66 74 77 61 72 65 20 76 69 |uter software vi|
00000080 61 20 74 65 6c 65 74 65 78 74 20 69 73 20 6e 6f |a teletext is no|
00000090 74 20 71 75 69 74 65 20 74 68 65 20 73 69 6d 70 |t quite the simp|
000000a0 6c 65 0d 0a 70 72 6f 63 65 73 73 20 69 74 20 6d |le..process it m|
000000b0 61 79 20 61 74 20 66 69 72 73 74 20 73 65 65 6d |ay at first seem|
000000c0 2e 20 49 6e 20 70 72 61 63 74 69 63 65 2c 20 6d |. In practice, m|
000000d0 61 6e 79 20 66 61 63 74 6f 72 73 20 68 61 76 65 |any factors have|
000000e0 20 74 6f 20 62 65 0d 0a 63 6f 6e 73 69 64 65 72 | to be..consider|
000000f0 65 64 20 69 6e 20 6f 72 64 65 72 20 74 6f 20 62 |ed in order to b|
00000100 72 6f 61 64 63 61 73 74 20 74 68 65 20 66 75 6c |roadcast the ful|
00000110 6c 20 72 61 6e 67 65 20 6f 66 20 63 6f 64 65 73 |l range of codes|
00000120 20 69 6e 63 6c 75 64 65 64 20 69 6e 0d 0a 74 65 | included in..te|
00000130 6c 65 73 6f 66 74 77 61 72 65 20 66 69 6c 65 73 |lesoftware files|
00000140 2e 20 54 68 69 73 20 6d 6f 64 75 6c 65 20 6c 6f |. This module lo|
00000150 6f 6b 73 20 61 74 20 73 6f 6d 65 20 6f 66 20 74 |oks at some of t|
00000160 68 65 20 70 72 6f 62 6c 65 6d 73 2c 20 61 6e 64 |he problems, and|
00000170 20 6f 66 66 65 72 73 0d 0a 70 72 61 63 74 69 63 | offers..practic|
00000180 61 6c 20 72 6f 75 74 69 6e 65 73 20 66 6f 72 20 |al routines for |
00000190 64 6f 77 6e 6c 6f 61 64 69 6e 67 20 61 6e 79 20 |downloading any |
000001a0 63 6f 72 72 65 63 74 6c 79 20 66 6f 72 6d 61 74 |correctly format|
000001b0 74 65 64 20 66 69 6c 65 73 20 66 72 6f 6d 20 61 |ted files from a|
000001c0 6e 79 0d 0a 74 65 6c 65 74 65 78 74 20 63 68 61 |ny..teletext cha|
000001d0 6e 6e 65 6c 2e 0d 0a 0d 0a 5f 5f 5f 5f 5f 5f 5f |nnel....._______|
000001e0 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f 5f |________________|
*
00000220 5f 5f 5f 0d 0a 0d 0a 54 65 6c 65 74 65 78 74 20 |___....Teletext |
00000230 49 6e 74 65 72 61 63 74 69 76 65 20 50 6f 72 67 |Interactive Porg|
00000240 72 61 6d 6d 69 6e 67 3a 0d 0a 0d 0a 41 64 76 61 |ramming:....Adva|
00000250 6e 63 65 64 20 54 65 6c 65 74 65 78 74 20 53 79 |nced Teletext Sy|
00000260 73 74 65 6d 2e 20 36 0d 0a 0d 0a 28 63 29 20 4a |stem. 6....(c) J|
00000270 2e 4a 2e 42 72 61 79 73 68 61 77 20 31 39 38 37 |.J.Brayshaw 1987|
00000280 0d 0a 0d 0a 54 65 6c 65 73 6f 66 74 77 61 72 65 |....Telesoftware|
00000290 20 66 69 6c 65 73 3a 0d 0a 0d 0a 0d 0a 43 6f 6d | files:......Com|
000002a0 70 75 74 65 72 20 73 6f 66 74 77 61 72 65 20 64 |puter software d|
000002b0 65 73 69 67 6e 65 64 20 66 6f 72 20 75 73 65 20 |esigned for use |
000002c0 77 69 74 68 20 61 6e 20 38 2d 62 69 74 20 63 6f |with an 8-bit co|
000002d0 6d 70 75 74 65 72 20 63 6f 6e 73 69 73 74 73 0d |mputer consists.|
000002e0 0a 65 6e 74 69 72 65 6c 79 20 6f 66 20 63 6f 64 |.entirely of cod|
000002f0 65 73 20 69 6e 20 74 68 65 20 72 61 6e 67 65 20 |es in the range |
00000300 26 30 30 20 74 6f 20 26 46 46 2c 20 6f 72 20 30 |&00 to &FF, or 0|
00000310 20 74 6f 20 32 35 35 2e 20 54 72 61 6e 73 6d 69 | to 255. Transmi|
00000320 73 73 69 6f 6e 20 6f 66 0d 0a 73 6f 66 74 77 61 |ssion of..softwa|
00000330 72 65 20 76 69 61 20 43 45 45 46 41 58 20 69 73 |re via CEEFAX is|
00000340 2c 20 74 68 65 72 65 66 6f 72 65 2c 20 74 68 65 |, therefore, the|
00000350 6f 72 65 74 69 63 61 6c 6c 79 20 65 61 73 79 2e |oretically easy.|
00000360 20 4a 75 73 74 20 72 65 70 6c 61 63 65 20 74 68 | Just replace th|
00000370 65 0d 0a 63 68 61 72 61 63 74 65 72 73 20 74 68 |e..characters th|
00000380 61 74 20 6d 61 6b 65 20 75 70 20 61 20 64 69 73 |at make up a dis|
00000390 70 6c 61 79 61 62 6c 65 20 70 61 67 65 20 77 69 |playable page wi|
000003a0 74 68 20 74 68 65 20 63 6f 64 65 73 2c 20 69 6e |th the codes, in|
000003b0 20 74 68 65 20 63 6f 72 72 65 63 74 0d 0a 73 65 | the correct..se|
000003c0 71 75 65 6e 63 65 2c 20 66 72 6f 6d 20 61 20 63 |quence, from a c|
000003d0 6f 6d 70 75 74 65 72 20 70 72 6f 67 72 61 6d 2e |omputer program.|
000003e0 0d 0a 0d 0a 55 6e 66 6f 72 74 75 6e 61 74 65 6c |....Unfortunatel|
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00000980 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 20 20 |.............. |
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*
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000009e0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
*
00000a00 20 4a 2e 4a 2e 42 72 61 79 73 68 61 77 20 31 39 | J.J.Brayshaw 19|
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00002550 20 74 68 65 6d 73 65 6c 76 65 73 20 63 61 6e 20 | themselves can |
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00002590 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d |................|
000025a0 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 20 |............... |
000025b0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
*
000025d0 20 50 61 67 65 20 34 0d 0a 0d 0a 0d 0a 0d 0a 0d | Page 4.........|
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000025f0 74 69 76 65 20 70 72 6f 67 72 61 6d 6d 69 6e 67 |tive programming|
00002600 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
*
00002620 20 20 4a 2e 4a 2e 42 72 61 79 73 68 61 77 20 31 | J.J.Brayshaw 1|
00002630 39 38 37 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 54 68 65 |987..........The|
00002640 20 52 54 46 20 64 65 63 6f 64 69 6e 67 20 61 6c | RTF decoding al|
00002650 67 6f 72 69 74 68 6d 3a 0d 0a 0d 0a 0d 0a 20 20 |gorithm:...... |
00002660 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 53 | S|
00002670 54 41 52 54 0d 0a 20 20 20 20 20 20 20 20 20 20 |TART.. |
00002680 20 20 20 20 20 20 20 20 20 7c 0d 0a 20 20 2b 2d | |.. +-|
00002690 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2b |---------------+|
000026a0 0d 0a 20 20 7c 20 20 20 20 20 20 20 20 20 20 20 |.. | |
000026b0 20 20 20 20 20 7c 0d 0a 20 20 7c 20 20 20 20 20 | |.. | |
000026c0 20 20 20 2b 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d | +------------|
000026d0 2d 2d 2d 2b 0d 0a 20 20 7c 20 20 20 20 20 20 20 |---+.. | |
000026e0 20 7c 20 47 65 74 20 62 79 74 65 20 20 20 20 20 | | Get byte |
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00002700 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2b |---------------+|
00002710 0d 0a 20 20 7c 20 20 20 20 20 20 20 20 20 20 20 |.. | |
00002720 20 20 20 20 20 7c 0d 0a 20 20 7c 20 20 20 20 20 | |.. | |
00002730 20 20 20 2b 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d | +------------|
00002740 2d 2d 2d 2b 0d 0a 20 20 7c 20 20 20 20 20 20 20 |---+.. | |
00002750 20 7c 20 4c 6f 6f 6b 20 75 70 20 74 68 65 20 20 | | Look up the |
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000027d0 20 20 7c 0d 0a 20 20 7c 20 20 20 20 20 20 20 20 | |.. | |
000027e0 20 20 20 20 20 20 20 20 2f 20 5c 20 20 20 20 20 | / \ |
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00002920 20 7c 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | |
00002930 4e 4f 20 7c 20 20 20 20 20 20 20 20 20 20 20 20 |NO | |
00002940 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
00002950 20 20 20 20 20 20 7c 0d 0a 20 20 7c 20 20 20 20 | |.. | |
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*
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00002ac0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
00002ad0 20 20 20 2f 20 45 6e 64 20 5c 20 20 59 45 53 0d | / End \ YES.|
00002ae0 0a 20 20 7c 20 20 20 20 20 20 20 20 20 20 20 20 |. | |
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00002b00 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
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*
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*
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00002de0 20 20 20 20 20 20 20 20 20 20 20 7c 20 20 20 20 | | |
00002df0 7c 20 47 65 74 20 6e 65 78 74 20 7c 0d 0a 20 20 || Get next |.. |
00002e00 7c 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 || |
00002e10 20 20 7c 20 20 20 20 20 20 20 20 20 20 20 20 20 | | |
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00002f40 20 20 20 20 20 20 20 20 50 61 67 65 20 35 0d 0a | Page 5..|
00002f50 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a |................|
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00002f80 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
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000065e0 6f 20 6d 61 79 0d 0a 6e 6f 74 20 62 65 20 61 73 |o may..not be as|
000065f0 20 73 75 63 63 65 73 73 66 75 6c 20 61 73 20 79 | successful as y|
00006600 6f 75 20 6d 69 67 68 74 20 69 6d 61 67 69 6e 65 |ou might imagine|
00006610 21 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d |!...............|
00006620 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d 0a 0d |................|
00006630 0a 0d 0a 0d 0a 20 20 20 20 20 20 20 20 20 20 20 |..... |
00006640 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | |
00006650 20 20 20 20 20 20 50 61 67 65 20 31 31 0d 0a 0d | Page 11...|
00006660 0a 0d 0a 0d 0a |.....|
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