Difference between revisions of "UVSG Satellite Data"

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(Command Modes)
(Command Modes)
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| Provides some settings, like GridMR, Sport, SBS, ClockCmd, and more that are written to config.dat.
 
| Provides some settings, like GridMR, Sport, SBS, ClockCmd, and more that are written to config.dat.
|  
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| Length specified in first byte of command. Checksum is strange?
 
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| Yes
 
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Revision as of 17:26, 17 June 2011

This was the format used by United Video Satellite Group to send data out at 2400 baud over a satellite feed. Many different types of information were sent out through this feed, including time/date information, system settings, channel listings, and system updates.

Tin has successfully reverse engineered parts of this format, and it is now 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.

Overview

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 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.

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! Some of the checksums were found from an Atari disassembly, and a few were found by running UVSG sample messages through UVSGXOR.

Command Name Initial Checksum Description Notes Atari Amiga
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
D  ? $BB  ?  ? No 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
N  ? $B1  ? Atari L92A4 Yes No
O  ? $B0  ? No checksum - send $00 $B0 immediately after - Atari L91BA (Amiga accepts as valid) Yes Yes
P Program $AF Program information 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
None 0x01
HILITESRC 0x02
SUMBYSRC 0x04
VIDEO_TAG_DISABLE 0x08
CAF_PPVSRC 0x10
DITTO 0x20
ALTHILITESRC 0x40
STEREO 0x80

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
ALTHILITEPROG 0x04
TAGPROG 0x08
SPORTSPROG 0x10
DVIEW_USED 0x20
REPEATPROG 0x40
PREVDAYSDATA 0x80