The MIL-STD1553 transceiver IC has differential pairs with the same pins . Should I connect them?The IC that i use holtic hi 2130 and I couldn't see any warning in datasheet about it. In the reference shematic it is clearly seen that it is connected to each other.Should i add a trace directly? any idea?
This is typically done when a single pin is not able to carry enough current, i.e., when the resistance of a single bond wire/pin/ball would be too high.
You must connect these pins together. (How exactly does not matter; your traces are much stronger than the bond wires.)
1553 is an old standard. It expects you to daisy chain devices together to make one giant bus. While not mandatory, 1553 implementation very strongly tends to be dual-redundant. If you check the 2130 product brief, you'll see it is acting as four devices: a bus controller, two remote terminals, and a bus monitor.
Two remote terminals is a deeply unusual design choice, unless you are hooking the same device into two different networks. I can't think of any actual examples, but I have heard that described as a way to bridge two different busses.
So. What you probably have is pins to connect to two, dual-redundant busses. I haven't dug into it, but I'd bet your SDK includes a way to attach each virtual device to each bus. Pick the bus you want to attach to, and connect to that.
Because of the way busses work in 1553, it probably won't do any harm to connect the two together, but it's still bad design. If you only hook up to one redundant bus-pair, you get slightly easier debugging and a few fewer failure paths. Also, you make future design changes easier.