UVSG Satellite Data

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This was the format used by United Video Satellite Group to send data out at over a satellite feed, launched some time between 1981 and 1985. 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.

DATA Format

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.

Initial Checksum

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 INCLUDING the 55 AA training and the ASCII value of the command letter. However at least in the Atari code, the 55 AA and command letter are not checksummed, instead the code is seeded with the value that would be arrived at if that calculation had been performed.

Command Modes

Some of this is conjecture and named according to clues found in the reverse-engineered code - it's subject to change and mistakes!

Command Name Description Notes Atari Amiga
A Box On Addresses the machines by select code, informing them to listen for commands Yes Yes
C Channel lineup Contains the channel lineup Divided by the receiving machine into a list of channel numbers, call letters, and sources. Yes Yes
c Source Attributes No Yes
D Diagnostic mode ? ? No Yes
E ? ? Atari L9118 (3 bytes - some kind of configuration bytes relating to CURDAY and NXTDAY?) - on Amiga, reads in a bunch of bytes... possibly related to select code? Yes Yes
F Configuration 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 new look config Provides some settings, like GridMR, Sport, SBS, ClockCmd, and more that are written to config.dat. Length specified in first byte of command. No Yes
g new local config avail also defines future DST information No Yes
H Download 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
h Download Same command as 'H' No Yes
I Weather ID Sets weather ID No Yes
i ? No Yes
J Order Information For pay-per-view channels No Yes
j Order Information For pay-per-view channels (likely newer format) No Yes
K Clock Sets the time centrally Requires ClockCmd to be 2 on Amiga version 9 Yes Yes
L Local text (aka Local Ad) Centrally provides an ad or message Yes Yes
M Mode ? Atari L9152 (reads 2 bytes) - on Amiga, reads 0 bytes and does NOTHING but increment the Cmds count Yes Yes
N ? ? Atari L92A4 Yes No
O Reset Blackout Clears program listings - but not immediately? Reads 0 bytes - send 00 B0 after Yes Yes
P Program info Program information Yes Yes
p Program attribute Program information Possibly newer format, example in NEWP test file No Yes
Q ? Not sure, probably has something to do with PPV channels No Yes
R Reset Reset/reboot all listening computers Yes Yes
S Script For laser-guide only
T Title Sets the guide title Yes No
t Color Local Ad Provides local ad data (identical to mode L, but unsupported on older software) No Yes
V Version ? Software upgrade/version check mechanism? No Yes
v PPV info ? No Yes
W Weather Data ? No Yes
w ? ? No Yes
x "x command" ? Has sub-commands? No Yes
Z ? ? Atari L9206 (12 configuration bytes read into 04E7 onwards) Yes No
$03 ? ? Atari L949F (hexadecimal 03) Yes No
! ($21) ? ? No Yes
% ($25) Save Data Saves/backs up data to disk the next time it gets a $BB command Analogous to one of the "Save Data" options under Special Functions, freezes guide for a few seconds while saving No Yes
+ ($2B) VCRplus
= ($3D) Download ? Same command as 'H' No Yes
$BB Box Off Tells all listening boxes to stop listening No checksum - send BB 00 FF 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
None 0x01
DITTO 0x20

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
None 0x01
Movie 0x02

L Command Syntax

0x4C [ad number, byte]
[text alignment byte] [line 1 text, string]
[text alignment byte] [line 2 text, string] (repeated for each desired line)
0x14 [ad beginning timeslot, 1-48] [ad ending timeslot, 1-48] (optional)
0x00 [checksum, byte]

Here is an example which sets the contents of the first ad:

55 AA 4C 01 18 42 45 46 4F 52 45 20 59 4F 55 20 56 49 45 57 2C 20 50 52 45 56 55 45 21 00 D1

The optional 0x14 (CTRL-T) sequence allows the command to limit the timeslots in which the ad appears. This is supported on Amiga only, and ignored on Atari.

NOTE: Sending 0x92 in place of the ad number causes all text ads to be reset. Example:

55 AA 4C 92 00 21
Text Alignment Bytes

The following text alignment bytes are supported:

Text Alignment Hex value
Center 0x18 (CTRL-X)
Left 0x19 (CTRL-Y)
Right 0x1A (CTRL-Z)
Crawl 0x0B (CTRL-K)

A new text alignment byte must be included for each new ad line. The byte 0x0B (CTRL-K) can be used on EPG Sr. to indicate that the ad should be used as a crawl ad instead of a scroll ad.

t Command Syntax

0x4C [ad number, byte]
[text alignment byte]
0x03 [background color byte] [foreground color byte] [text, string] (repeated for each desired new color)
0x14 [ad beginning timeslot, 1-48] [ad ending timeslot, 1-48] (optional)
0x00 [checksum, byte]

The 0x03 (CTRL-C) sequence can be included as many times as desired, and defines the colors to be used for the characters which follow the sequence.


55 AA 74 05 18 03 36 33 50 72 65 76 75 65 20 03 35 34 46 69 72 73 74 21 00 E8

NOTE: The 't' command and 'L' command are identical and handled the same by ESQ. Using 't' as the command byte instead of 'L' guarantees that color ads are not received by older software that doesn't support color ads (like Atari), since older software doesn't recognize the 't' command.

t Commmand Colors
Color name Hex value
Transparent 0x30
White 0x31
Black 0x32
Yellow 0x33
Red 0x34
Light blue 0x35
Grey 0x36
Blue 0x37

CTRL Format

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.

CTRL Commands

Command Control Name Length Description
$01 A ? Branches based on the first byte it receives - looks like it has "sub-commands"
$02 B ?
$03 C ? 0 bytes Different than the other commands - not parsed
$04 D Set Position 1 byte Sets CTRLEvent_Position to 1 if byte is 'L' or 0 if 'R', if neither, CTRLEvent_Position is toggled
$05 E Event 2 bytes First byte corresponds to right side, second corresponds to left - seems to set a "mode" for the overlay of each side
$07 G Resume Scroll 0 bytes Resumes listing scroll (analogous to pressing 's')
$0B K Clock Slightly different syntax than DATA, only works when ClockCmd is 1
$0C L ? Has something to do with what program is displayed in the overlay in E mode
$0D M End of Command
$0F O ? Blanks out screen - probably used to set some stuff
$10 P Stop Scroll 0 bytes Stops listing scroll (analogous to Control-S)
$11 Q ?
$14 T ? 1 byte? Sets some internal variable
$16 V ?

Mode A Sub-Commands

Byte ASCII Name Length Description
$31 1
$33 3
$34 4
$35 5
$36 6
$37 7
$44 D
$46 F
$57 W Weather 0 bytes Show weather info?