Hi TI support engineer:
We have been trying to use Des-Ser 913/914 in a mutltiple -drop bus topology, although we understand Des-Ser 913/914 and FPD-LINK is designed for point-to-point communication. Now we see mto hit the end wall, and looking for your opinion and suggestion. Issues described as follwoing:
We need to acquire image data from mutiple cameras (with Ser913 on each board) (say ~16 camera board) with low system cost.
So our oringal plan is to use one DERS914 to communciate with one of the 16 camera boars at a time, by only powering on one specific camera board at a time. There is a MOSFET bus switch on each camera board, which apears open(high impedance) to the bus. The FPD-LINK bus is made of twisted pair wire, total length is 10meter. The mutiple camera boards are all hooked up to this bus all the time .Again, we wished it could work by using the approach "only power only one camera board(with Ser913" + bus switch"., Please refer to attahced drawing.
But we are having problem now, which seems caused by signal reflection. The MOSTFET bus switch appear hign Z when not powerd on, which as expected, then it seems the signal reflextion on the bus(i.e FPD-LINK) is the trouble-maker. At 10 meter bus length, nothing worked( neither one camera nor mutiple camera).
At much shorter bus length (say 1meter,,instead of 10 meter) with more than camera ( 2 or more) nothing worked either.
But, when only use one camera board at the end point of the 1meter cable, the system worked (which mean our software and hardware are OK). The interesting thing is: at 1meter bus, if we put the only one camera board at the middle point of the cable ( ~50cm) leaving another half length (~50cm) open end, then the system stop working again, This seems saying the extra length bus cable casued reflection. Which means evethough we have a bus switch on each board, this topology will still not work.
Do you have any suggestion to our topology of such a bus usage? Any help is much appreciated.
We do not want to add a MCU on each camera board.
Thanks in advance.
Tom
