noz
December 07, 2007 06:31 pm
Hi Ciaran,
The S1 matrix is quite different to the S2. The S1 works on a very simple principle. It has, say, 20 pins. If you short each pin in turn to earth you get a different alarm on the display. The little chip inside has the necessary text already programmed inside so as it detects each pin shorted to earth it brings up the associated message. It has no data comms whatsoever.
For the most part the S2 dot matrix operates the same way. It too has, say, 20 pins each of which produces a different text message when grounded. However, most importantly it has 2 additional pins. These are connected to two pins on the back of the radio. The interconnecting cable carries RDS information on CAN or VAN protocol from the radio to the dot matrix. Thats how you can see the name of the radio station or the frequency or the 'seek' text. In this case the text is not stored in the chip inside the display. The message is physically transmitted from the radio to the display. By piggybacking on the comms pair, using the right protocol, you can get the display to say almost anything you like.
In both cases the messages have a pre-programmed priority order so more serious alarms are displayed rather than a less serious alarm. As most people know, an ABS alarm masks all others and won't go away until the problem is fixed. In the S2 display any alarm is more important than radio station information therefore the alarms are given priority over radio info.
Hope that clears it up and saves you hours of tinkering with a non-comms S1 display. When I get home from work I'll post the website with the display comms project (although I'm sure I've already posted it on club-xm somewhere).
Found it:
http://club-xm.com/forum/index.php?showtopic=603cheers
noz