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ATS/T\ATS13

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\ATS13
Read OK: ✔
File size: 1B1A bytes
Load address: 0000
Exec address: 0000
File contents


Interactive programming                                  J.J.Brayshaw 1987




ATS13: *TELESOFT
================

When pages are received from transmission using the normal ATS page
transfer facilities, they are in "raw data" format and need further
processing before being displayed. This was not necessary with the Acorn
TFS software, as any such processing was carried out before transferring
the page to computer memory. This type of page transfer is also available
with ATS, but it is not (yet) common knowledge ...

__________________________________________________________________________


The Advanced Teletext System software includes the command *TRANSFER to
capture a teletext page from a broadcast and transfer the data received
into computer memory for further processing. This page data can be used to
form a display if required, and ATS includes a *DISPLAY command to
facilitate this.

To display a page from the captured page data may seem a very simple
operation, but studying the exact content of a transmitted page shows that
some "intelligence" is required to create a full teletext page from the
data supplied.

Each row (or packet) broadcast consists of 42 bytes - but only 40 bytes
can be displayed on screen. The first two bytes are the magazine number
and the row number. In fact, 45 bytes are actually transmitted, but the
adapter itself needs the first three to identify a row of teletext as such
(and not just another tv picture line), and so does not pass them on to
ATS.

There are a few important points to note when dealing with the "raw" page
data:

 (a) the packets for a page may be transmitted in any order.

 (b) packets containing 40 spaces need not be transmitted.

 (c) the second row of a double-height display is not normally
     transmitted.

 (d) some packets may be transmitted more than once.

Such situations need to be dealt with by any teletext receiver in order to
produce the intended display. For example, untransmitted packets should be
considered as either 40 spaces or a copy of the previous row, depending on
whether the previous row contains a double-height character or not.





                                  Page 1








Interactive programming                                  J.J.Brayshaw 1987




There are, in fact, two different ways in which the data for a page can be
transferred into memory by ATS, and any subsequent processing is different
for each format.

*TTXON enables telesoftware interrupts (i.e. the ATS responds to messages
sent to the computer by the adapter). In this state, any page transferred
is in the "default" format of 42 bytes per row, almost exactly as
transmitted. The only processing carried out by the adapter/ATS in this
format is the exclusion of the first three bytes of each packet (the clock
run-in and the framing code) and de-hamming of some of the hamming-coded
bytes.

An alternative page capture format is provided by the command *TELESOFT.
This enables reception of page data in a ready-to-display form, with
untransmitted rows generated correctly, each packet consisting of just the
40 displayable bytes of each row, and the packets sorted into their
correct order. The command should replace the *TTXON command within your
program. However, due a slight problem with ATS version 2.50, it is better
to issue both commands when requesting this format, using *TTXON followed
by *TELESOFT (or its minimum abbreviation *TELES.) before issuing any
channel or page requests.

This mode of data transfer was included in ATS to provide a measure of
compatibility with the older TFS ROM. The latter always transferred pages
as 24 packets of 40 bytes each, and no option was available to transfer
the full packet data of 42 bytes. With ATS, this command when used with
the *TRANSFER command, will emulate the TFS. However, it can be extended
to receive as many packets as are transmitted for the selected page by
using *TRANSFER followed by *DATA, as in the accompanying program.

The *DISPLAY routine is self-adjusting to cope with the page being
transferred in either mode.

*TELESOFT has become a very useful command with ATS as it reduces the
amount of page data processing required, makes it more reliable to find
the precise position of data within a specific page and makes it easier to
calculate the memory space requirements for any page transfer.

__________________________________________________________________________

B/ATS13 uses a Mode 0 screen to display exactly what has been received in
either *TTXON or *TELESOFT mode. The program is set to look at ITV Oracle,
page 100. This page is transmitted with the packets out of order (look at
where packet 27 is broadcast!) and shows how *TTXON with *DATA transfers
the packets in the order they are transmitted, whilst *TELESOFT with *DATA
transfers the page with packet 27 in the correct location, double-height
packets duplicated correctly, and non-broadcast packets replaced with
spaces (unless used for double-height rows).




                                  Page 2








Interactive programming                                  J.J.Brayshaw 1987





In the first display of the program, the first digit is the magazine
number (taken from the first byte of the packet), the second number is the
packet (row) number, taken from the second byte of the packet. Both of
these have been interpreted as ASCII characters, as they are actually
transmitted as the binary code of the appropriate value (i.e. if the
magazine number is two, this is transmitted as CHR$(2) which has been
interpreted for the display as the digit "2"). Suitable spacing has been
added to clarify the display. The remaining bytes are the 40 data bytes
from the packet. Control codes etc. have been altered to spaces to avoid
problems with the Mode 0 display.

It is interesting to alter the program to look at BBC2, page 700. This
should show four different packet 27's, plus packets 24 and 25 (in fact
the maximum possible data for a Level 1 FLOF teletext transmission).
These additional packets 27's are uniquely identified by the first data
byte, and carry the details of the full 24 page links.

Beware, however, as even though *DATA also transfers packet 27, the ATS
OSWORD call to check the CRC, will fail because the page is no longer in
the expected format. (See ATS01 for details of the CRC calculations).

Using the *TELESOFT command offers savings in both space and processing,
and can be used in most teletext applications software for limited
purposes. It cannot be used where some of the more advanced teletext
features, including page data integrity checking or page link decoding,
are needed. For such applications, the *TTXON mode must be used, involving
additional processing within your own software to extract the precise
information required, but keeping full control of the data with the
programmer.






















                                  Page 3





00000000  0d 0d 0d 49 6e 74 65 72  61 63 74 69 76 65 20 70  |...Interactive p|
00000010  72 6f 67 72 61 6d 6d 69  6e 67 20 20 20 20 20 20  |rogramming      |
00000020  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
00000030  20 20 20 20 20 20 20 20  20 20 20 20 4a 2e 4a 2e  |            J.J.|
00000040  42 72 61 79 73 68 61 77  20 31 39 38 37 0d 0d 0d  |Brayshaw 1987...|
00000050  0d 0d 41 54 53 31 33 3a  20 2a 54 45 4c 45 53 4f  |..ATS13: *TELESO|
00000060  46 54 0d 3d 3d 3d 3d 3d  3d 3d 3d 3d 3d 3d 3d 3d  |FT.=============|
00000070  3d 3d 3d 0d 0d 57 68 65  6e 20 70 61 67 65 73 20  |===..When pages |
00000080  61 72 65 20 72 65 63 65  69 76 65 64 20 66 72 6f  |are received fro|
00000090  6d 20 74 72 61 6e 73 6d  69 73 73 69 6f 6e 20 75  |m transmission u|
000000a0  73 69 6e 67 20 74 68 65  20 6e 6f 72 6d 61 6c 20  |sing the normal |
000000b0  41 54 53 20 70 61 67 65  0d 74 72 61 6e 73 66 65  |ATS page.transfe|
000000c0  72 20 66 61 63 69 6c 69  74 69 65 73 2c 20 74 68  |r facilities, th|
000000d0  65 79 20 61 72 65 20 69  6e 20 22 72 61 77 20 64  |ey are in "raw d|
000000e0  61 74 61 22 20 66 6f 72  6d 61 74 20 61 6e 64 20  |ata" format and |
000000f0  6e 65 65 64 20 66 75 72  74 68 65 72 0d 70 72 6f  |need further.pro|
00000100  63 65 73 73 69 6e 67 20  62 65 66 6f 72 65 20 62  |cessing before b|
00000110  65 69 6e 67 20 64 69 73  70 6c 61 79 65 64 2e 20  |eing displayed. |
00000120  54 68 69 73 20 77 61 73  20 6e 6f 74 20 6e 65 63  |This was not nec|
00000130  65 73 73 61 72 79 20 77  69 74 68 20 74 68 65 20  |essary with the |
00000140  41 63 6f 72 6e 0d 54 46  53 20 73 6f 66 74 77 61  |Acorn.TFS softwa|
00000150  72 65 2c 20 61 73 20 61  6e 79 20 73 75 63 68 20  |re, as any such |
00000160  70 72 6f 63 65 73 73 69  6e 67 20 77 61 73 20 63  |processing was c|
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00000190  68 65 20 70 61 67 65 20  74 6f 20 63 6f 6d 70 75  |he page to compu|
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000001c0  61 6e 73 66 65 72 20 69  73 20 61 6c 73 6f 20 61  |ansfer is also a|
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000001e0  53 2c 20 62 75 74 20 69  74 20 69 73 20 6e 6f 74  |S, but it is not|
000001f0  20 28 79 65 74 29 20 63  6f 6d 6d 6f 6e 20 6b 6e  | (yet) common kn|
00000200  6f 77 6c 65 64 67 65 20  2e 2e 2e 0d 0d 5f 5f 5f  |owledge .....___|
00000210  5f 5f 5f 5f 5f 5f 5f 5f  5f 5f 5f 5f 5f 5f 5f 5f  |________________|
*
00000250  5f 5f 5f 5f 5f 5f 5f 0d  0d 0d 54 68 65 20 41 64  |_______...The Ad|
00000260  76 61 6e 63 65 64 20 54  65 6c 65 74 65 78 74 20  |vanced Teletext |
00000270  53 79 73 74 65 6d 20 73  6f 66 74 77 61 72 65 20  |System software |
00000280  69 6e 63 6c 75 64 65 73  20 74 68 65 20 63 6f 6d  |includes the com|
00000290  6d 61 6e 64 20 2a 54 52  41 4e 53 46 45 52 20 74  |mand *TRANSFER t|
000002a0  6f 0d 63 61 70 74 75 72  65 20 61 20 74 65 6c 65  |o.capture a tele|
000002b0  74 65 78 74 20 70 61 67  65 20 66 72 6f 6d 20 61  |text page from a|
000002c0  20 62 72 6f 61 64 63 61  73 74 20 61 6e 64 20 74  | broadcast and t|
000002d0  72 61 6e 73 66 65 72 20  74 68 65 20 64 61 74 61  |ransfer the data|
000002e0  20 72 65 63 65 69 76 65  64 0d 69 6e 74 6f 20 63  | received.into c|
000002f0  6f 6d 70 75 74 65 72 20  6d 65 6d 6f 72 79 20 66  |omputer memory f|
00000300  6f 72 20 66 75 72 74 68  65 72 20 70 72 6f 63 65  |or further proce|
00000310  73 73 69 6e 67 2e 20 54  68 69 73 20 70 61 67 65  |ssing. This page|
00000320  20 64 61 74 61 20 63 61  6e 20 62 65 20 75 73 65  | data can be use|
00000330  64 20 74 6f 0d 66 6f 72  6d 20 61 20 64 69 73 70  |d to.form a disp|
00000340  6c 61 79 20 69 66 20 72  65 71 75 69 72 65 64 2c  |lay if required,|
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000003e0  75 64 79 69 6e 67 20 74  68 65 20 65 78 61 63 74  |udying the exact|
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00000420  69 6e 74 65 6c 6c 69 67  65 6e 63 65 22 20 69 73  |intelligence" is|
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00000480  61 63 6b 65 74 29 20 62  72 6f 61 64 63 61 73 74  |acket) broadcast|
00000490  20 63 6f 6e 73 69 73 74  73 20 6f 66 20 34 32 20  | consists of 42 |
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00000500  72 0d 61 6e 64 20 74 68  65 20 72 6f 77 20 6e 75  |r.and the row nu|
00000510  6d 62 65 72 2e 20 49 6e  20 66 61 63 74 2c 20 34  |mber. In fact, 4|
00000520  35 20 62 79 74 65 73 20  61 72 65 20 61 63 74 75  |5 bytes are actu|
00000530  61 6c 6c 79 20 74 72 61  6e 73 6d 69 74 74 65 64  |ally transmitted|
00000540  2c 20 62 75 74 20 74 68  65 0d 61 64 61 70 74 65  |, but the.adapte|
00000550  72 20 69 74 73 65 6c 66  20 6e 65 65 64 73 20 74  |r itself needs t|
00000560  68 65 20 66 69 72 73 74  20 74 68 72 65 65 20 74  |he first three t|
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00000590  73 75 63 68 0d 28 61 6e  64 20 6e 6f 74 20 6a 75  |such.(and not ju|
000005a0  73 74 20 61 6e 6f 74 68  65 72 20 74 76 20 70 69  |st another tv pi|
000005b0  63 74 75 72 65 20 6c 69  6e 65 29 2c 20 61 6e 64  |cture line), and|
000005c0  20 73 6f 20 64 6f 65 73  20 6e 6f 74 20 70 61 73  | so does not pas|
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00000650  6d 61 79 20 62 65 20 74  72 61 6e 73 6d 69 74 74  |may be transmitt|
00000660  65 64 20 69 6e 20 61 6e  79 20 6f 72 64 65 72 2e  |ed in any order.|
00000670  0d 0d 20 28 62 29 20 70  61 63 6b 65 74 73 20 63  |.. (b) packets c|
00000680  6f 6e 74 61 69 6e 69 6e  67 20 34 30 20 73 70 61  |ontaining 40 spa|
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000006a0  74 72 61 6e 73 6d 69 74  74 65 64 2e 0d 0d 20 28  |transmitted... (|
000006b0  63 29 20 74 68 65 20 73  65 63 6f 6e 64 20 72 6f  |c) the second ro|
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00000700  20 28 64 29 20 73 6f 6d  65 20 70 61 63 6b 65 74  | (d) some packet|
00000710  73 20 6d 61 79 20 62 65  20 74 72 61 6e 73 6d 69  |s may be transmi|
00000720  74 74 65 64 20 6d 6f 72  65 20 74 68 61 6e 20 6f  |tted more than o|
00000730  6e 63 65 2e 0d 0d 53 75  63 68 20 73 69 74 75 61  |nce...Such situa|
00000740  74 69 6f 6e 73 20 6e 65  65 64 20 74 6f 20 62 65  |tions need to be|
00000750  20 64 65 61 6c 74 20 77  69 74 68 20 62 79 20 61  | dealt with by a|
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00000800  69 6f 75 73 20 72 6f 77  2c 20 64 65 70 65 6e 64  |ious row, depend|
00000810  69 6e 67 20 6f 6e 0d 77  68 65 74 68 65 72 20 74  |ing on.whether t|
00000820  68 65 20 70 72 65 76 69  6f 75 73 20 72 6f 77 20  |he previous row |
00000830  63 6f 6e 74 61 69 6e 73  20 61 20 64 6f 75 62 6c  |contains a doubl|
00000840  65 2d 68 65 69 67 68 74  20 63 68 61 72 61 63 74  |e-height charact|
00000850  65 72 20 6f 72 20 6e 6f  74 2e 0d 0d 0d 0d 0d 0d  |er or not.......|
00000860  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
*
00000880  20 20 50 61 67 65 20 31  0d 0d 0d 0d 0d 0d 0d 0d  |  Page 1........|
00000890  0d 49 6e 74 65 72 61 63  74 69 76 65 20 70 72 6f  |.Interactive pro|
000008a0  67 72 61 6d 6d 69 6e 67  20 20 20 20 20 20 20 20  |gramming        |
000008b0  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
000008c0  20 20 20 20 20 20 20 20  20 20 4a 2e 4a 2e 42 72  |          J.J.Br|
000008d0  61 79 73 68 61 77 20 31  39 38 37 0d 0d 0d 0d 0d  |ayshaw 1987.....|
000008e0  54 68 65 72 65 20 61 72  65 2c 20 69 6e 20 66 61  |There are, in fa|
000008f0  63 74 2c 20 74 77 6f 20  64 69 66 66 65 72 65 6e  |ct, two differen|
00000900  74 20 77 61 79 73 20 69  6e 20 77 68 69 63 68 20  |t ways in which |
00000910  74 68 65 20 64 61 74 61  20 66 6f 72 20 61 20 70  |the data for a p|
00000920  61 67 65 20 63 61 6e 20  62 65 0d 74 72 61 6e 73  |age can be.trans|
00000930  66 65 72 72 65 64 20 69  6e 74 6f 20 6d 65 6d 6f  |ferred into memo|
00000940  72 79 20 62 79 20 41 54  53 2c 20 61 6e 64 20 61  |ry by ATS, and a|
00000950  6e 79 20 73 75 62 73 65  71 75 65 6e 74 20 70 72  |ny subsequent pr|
00000960  6f 63 65 73 73 69 6e 67  20 69 73 20 64 69 66 66  |ocessing is diff|
00000970  65 72 65 6e 74 0d 66 6f  72 20 65 61 63 68 20 66  |erent.for each f|
00000980  6f 72 6d 61 74 2e 0d 0d  2a 54 54 58 4f 4e 20 65  |ormat...*TTXON e|
00000990  6e 61 62 6c 65 73 20 74  65 6c 65 73 6f 66 74 77  |nables telesoftw|
000009a0  61 72 65 20 69 6e 74 65  72 72 75 70 74 73 20 28  |are interrupts (|
000009b0  69 2e 65 2e 20 74 68 65  20 41 54 53 20 72 65 73  |i.e. the ATS res|
000009c0  70 6f 6e 64 73 20 74 6f  20 6d 65 73 73 61 67 65  |ponds to message|
000009d0  73 0d 73 65 6e 74 20 74  6f 20 74 68 65 20 63 6f  |s.sent to the co|
000009e0  6d 70 75 74 65 72 20 62  79 20 74 68 65 20 61 64  |mputer by the ad|
000009f0  61 70 74 65 72 29 2e 20  49 6e 20 74 68 69 73 20  |apter). In this |
00000a00  73 74 61 74 65 2c 20 61  6e 79 20 70 61 67 65 20  |state, any page |
00000a10  74 72 61 6e 73 66 65 72  72 65 64 0d 69 73 20 69  |transferred.is i|
00000a20  6e 20 74 68 65 20 22 64  65 66 61 75 6c 74 22 20  |n the "default" |
00000a30  66 6f 72 6d 61 74 20 6f  66 20 34 32 20 62 79 74  |format of 42 byt|
00000a40  65 73 20 70 65 72 20 72  6f 77 2c 20 61 6c 6d 6f  |es per row, almo|
00000a50  73 74 20 65 78 61 63 74  6c 79 20 61 73 0d 74 72  |st exactly as.tr|
00000a60  61 6e 73 6d 69 74 74 65  64 2e 20 54 68 65 20 6f  |ansmitted. The o|
00000a70  6e 6c 79 20 70 72 6f 63  65 73 73 69 6e 67 20 63  |nly processing c|
00000a80  61 72 72 69 65 64 20 6f  75 74 20 62 79 20 74 68  |arried out by th|
00000a90  65 20 61 64 61 70 74 65  72 2f 41 54 53 20 69 6e  |e adapter/ATS in|
00000aa0  20 74 68 69 73 0d 66 6f  72 6d 61 74 20 69 73 20  | this.format is |
00000ab0  74 68 65 20 65 78 63 6c  75 73 69 6f 6e 20 6f 66  |the exclusion of|
00000ac0  20 74 68 65 20 66 69 72  73 74 20 74 68 72 65 65  | the first three|
00000ad0  20 62 79 74 65 73 20 6f  66 20 65 61 63 68 20 70  | bytes of each p|
00000ae0  61 63 6b 65 74 20 28 74  68 65 20 63 6c 6f 63 6b  |acket (the clock|
00000af0  0d 72 75 6e 2d 69 6e 20  61 6e 64 20 74 68 65 20  |.run-in and the |
00000b00  66 72 61 6d 69 6e 67 20  63 6f 64 65 29 20 61 6e  |framing code) an|
00000b10  64 20 64 65 2d 68 61 6d  6d 69 6e 67 20 6f 66 20  |d de-hamming of |
00000b20  73 6f 6d 65 20 6f 66 20  74 68 65 20 68 61 6d 6d  |some of the hamm|
00000b30  69 6e 67 2d 63 6f 64 65  64 0d 62 79 74 65 73 2e  |ing-coded.bytes.|
00000b40  0d 0d 41 6e 20 61 6c 74  65 72 6e 61 74 69 76 65  |..An alternative|
00000b50  20 70 61 67 65 20 63 61  70 74 75 72 65 20 66 6f  | page capture fo|
00000b60  72 6d 61 74 20 69 73 20  70 72 6f 76 69 64 65 64  |rmat is provided|
00000b70  20 62 79 20 74 68 65 20  63 6f 6d 6d 61 6e 64 20  | by the command |
00000b80  2a 54 45 4c 45 53 4f 46  54 2e 0d 54 68 69 73 20  |*TELESOFT..This |
00000b90  65 6e 61 62 6c 65 73 20  72 65 63 65 70 74 69 6f  |enables receptio|
00000ba0  6e 20 6f 66 20 70 61 67  65 20 64 61 74 61 20 69  |n of page data i|
00000bb0  6e 20 61 20 72 65 61 64  79 2d 74 6f 2d 64 69 73  |n a ready-to-dis|
00000bc0  70 6c 61 79 20 66 6f 72  6d 2c 20 77 69 74 68 0d  |play form, with.|
00000bd0  75 6e 74 72 61 6e 73 6d  69 74 74 65 64 20 72 6f  |untransmitted ro|
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ATS/T\ATS13.m0
ATS/T\ATS13.m1
ATS/T\ATS13.m2
ATS/T\ATS13.m4
ATS/T\ATS13.m5

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