LVDS
tuxman
Posts: 9
in Propeller 2
How about including LVDS as option for I/O pins?
Comments
Is there something you'd like to connect to that uses LVDS?
the down side is that if you add LVDS to the board your kind of stuck with the traces wired to which ever pins you connect them to. so if you wanted to use pins 22 and 23 (or whatever pins are used for LVDS) you would always have a matched pair on those pins. Not a bad thing if you have lots of pins.
4 to 8 pairs would let you run all kinds of things.
Parts with CMOS out only, can Tx to LVDS with resistor pads, to reduce the swing and shift toward 0v.
Parts to Rx LVDS need a Differential Comparator, with modest hysteresis.
I'm unclear if the USB side of P2 implemented the Differential Comparator ?
There is a differential comparator in each pin that was intended to suffice for USB, but I can't remember at the moment if our USB implementation precludes its use.
You mean it is not generally available ?
What is the Tpd and Common mode range of that differential comparator ?
There is a M-LVDS bus, which is rather like a lower-swing version of RS485, usually used more locally and at higher speeds.
P2 is not going to get to full M-LVDS speed, but might usefully do 50~100MHz ? depends on the differential comparator.
The comparator works from 10mV differential and its range is 0.3V beyond the rails.
It can be enabled via pin mode. I don't have the details with me, but the OnSemi shuttle finished and they will package 100 dies next week. Then, we will make a board for the Prop123-A9 and have full access to TWO Prop2 I/O pins.
Swing wise, that is better than most LVDS, which use P-MOS inputs, so are not rail-rail.
Wahoo..
Speed of the differential comparator will be interesting.
I remember that with 100mV of differential, it's useful to 30MHz.