Rise/fall time for serial com

[borinsm]

I am scoping the data on a one wire open collector two direction signal, which I don't know what standard it's using or if it's just proprietary, but the rising edge looks somewhat weird to me.

It's running at 115.2k so the bit rate is around 8.7 uS, and the scope is measuring the rise time as 2.5 uS which seems slow.

I was wondering if there's a rule of thumb like a certain percentage of bit rate should be the transition time?

Also, in general suppose on that same data line, if I were to reduce the communication to 4800 bps which is drastically slower rate, should I expect the rise time to change, or would that be an inherent property of the hardware regardless of the bit rate since bit rate only controls how long it stays in its state, but it still has to "get" to that state the same way?
I was thinking if 2.5 uS is a constant in this circuit, by slowing down the bit rate I'd make the circuit more immune to it?

 

[Nigel Goodwin]

Rise time is usually dependent on the pullup resistor employed, lower value faster rise time.

 

[BrownOut]

The rise time will depend on the physical medium over which the signal travels. So, it's determined by transmission line impeadence, node capacitance, drive strength, etc. Changing the bit rate will not effect these determinates, so you will end up with more of your pulse at a stable level. Whether or not that actually makes you less immune to bit errors is another thing.