UVSG Satellite Data
This was the format used by United Video Satellite Group to send data out at over a satellite feed. The baud rate was initially 2400, although the speed may have been increased to 9600 baud towards the end. Many different types of information were sent out through this feed, including time/date information, system settings, channel listings, and system updates. The format was broadcast until at least 2002 (to support Sneak Prevue and remaining installations of EPG Jr.), but may even have lasted until 2005.
Tin and AriX have successfully reverse engineered parts of this format, and it is possible to send our own messages to emulated or real EPG/Prevue machines over serial. Additionally, some test files received from an ex-UV employee have helped to further the reverse engineering effort.
Every box on message always starts with the header "55 AA", followed by a select code, a 00, and a checksum. A command is started with a "55 AA", then a byte indicating which mode of command is being sent out, then the data of the command, which is usually followed by checksum.
For example, here are two commands that will tell an EPG machine to listen, then change its title to "PREVUE GUIDE":
55 AA 41 2A 00 94 55 AA 54 50 52 45 56 55 45 20 47 55 49 44 45 00 D0
In this example, the select code being addressed is 2A, or the ASCII code for an asterisk (*). This means every machine that is connected to the satellite feed will act on this command. Then, a 00 to terminate the string, and a checksum (94). After the 55 AA, you see the mode byte (54, or T for Title), and then an ASCII string (PREVUE GUIDE). Lastly, there is another 00 to terminate the string, and D0, the checksum for the entire string.
Most commands have a checksum that is calculated on all the bytes of the data part of the command. This is sent over the serial port and compared to the correct value by the receiving machine. If the checksum does not match, the computer discards the whole command. The checksum is calculated by bitwise XOR of each byte of data within the command excluding the command letter itself. Each command has its own hardcoded seed checksum which is loaded as the initial value of the checksum as soon as the initial command letter is recieved.
Some of this is conjecture and named according to clues found in the reverse-engineered code - it's subject to change and mistakes! Some of the checksums were found from an Atari disassembly, and a few were found by running UVSG sample messages through UVSGXOR.
|A||Box On||$BE||Addresses the machines by select code, informing them to listen for commands||Yes||Yes|
|C||Channel||$BC||Contains the channel lineup||Divided by the receiving machine into a list of channel numbers, call letters, and sources.||Yes||Yes|
|E||?||$BA||?||Atari L9118 (3 bytes - some kind of configuration bytes relating to CURDAY and NXTDAY?)||Yes||Yes|
|F||Configuration||$B9||Gives the receiving machine information about its location, local time, settings, ads, and more.||Same syntax on both Atari and Amiga, just a lot of unused values on Atari.||Yes||Yes|
|f||Config.dat||??||Provides some settings, like GridMR, Sport, SBS, ClockCmd, and more that are written to config.dat.||Length specified in first byte of command. Checksum is strange?||No||Yes|
|g||?||$98||Defines future DST information||No||Yes|
|H||Download||$B7||Can be used to write a file to disk, likely other Amiga maintenance tasks as well||Exact same command is also available under 'h' and '='||No||Yes|
|J||Order Information||$B5||For pay-per-view channels||No||Yes|
|j||Order Information||$95||For pay-per-view channels||(likely newer format)||No||Yes|
|K||Clock||$AB||Sets the time centrally||Requires ClockCmd to be 2 on Amiga||Yes||Yes|
|L||Ad||$B3||Centrally provides an ad or message||Seems to crash Prevue Grid if there is already ad in a slot, maybe bad syntax||Yes||Yes|
|M||?||$B2||?||Atari L9152 (reads 2 bytes)||Yes||Yes|
|O||?||$B0||?||No checksum - send $00 $B0 immediately after - Atari L91BA (Amiga accepts as valid)||Yes||Yes|
|p||Program||$8F||Program information||Possibly newer format, example in NEWP test file||No||Yes|
|Q||?||$AE||Not sure, probably has something to do with PPV channels||No||Yes|
|R||Reset||$AD||Reset computer||No checksum - send $00 $AD immediately after.||Yes||Yes|
|T||Title||$AB||Sets the guide title||Only applicable to EPG, but recognized by Prevue Grid as a valid command||Yes||Yes|
|Z||?||$A5||?||Atari L9206 (12 configuration bytes read into 04E7 onwards)||Yes||No|
|$03||?||?||?||Atari L949F (hexadecimal 03)||Yes||No|
|$BB||Box Off||$44||Tells all listening boxes to stop listening||No checksum - send $BB $00 $FF immediately after||Yes||Yes|
Known Command Syntax
C Command Syntax
0x43 [Julian day, byte] 0x12 [flags, byte] [6-character source, string] 0x11 [Channel #, string] 0x01 [5- to 6-character channel name, string] 0x00 [checksum, byte]
NOTE: On EPG Jr. the channel name has a limit of 5 characters
C Commmand Flags
|Flag name||Hex value|
P Command Syntax
0x50 [Timeslot 1-48, hex] [Julian day, hex] [6-character source, string] 0x12 [flags, byte] [Program name, string] 0x00 [checksum, byte]
P Commmand Flags
|Flag name||Hex value|
In 1988, with the introduction of Prevue Guide, a second, 110-baud feed called CTRL was added.
In the CTRL format, there is no initial 55 AA to start a command. Commands are begun right away with a mode byte, which is a number from 0 to 16 (instead of an ASCII value). Next, the body of the command is sent, followed by a $0D, and then the message checksum, which uses the same format as the DATA feed. The CTRL format has not yet been fully reverse engineered, but more information can be found [here http://ariweinstein.com/prevue/viewtopic.php?f=5&t=140&start=20#p1536].