SN65HVD1473: RS-485 tranceiver schematic (SN65HVD1473)

The EVM has many testing/debugging options that you do not actually need.

R12/R13 allow you to pull the bus lines to some voltages called "VCM_Z"/"VCM_Y". This is usually not needed for the SN65HVD1473, but if you have some receiver without fail-safe inputs on the bus, then it might be useful to have one set of fail-safe resistors somewhere on the bus.

C10 appears to be a low-pass filter. You should not try to slow down 20 Mbps signals.

Hi Ali,

What Clemens has indicated for the R12/R13 resistors is correct.

The C10 capacitor is used as a low pass filter - but mainly used to help attenuate higher frequency noise. Some designers do like adding these to help with higher frequency noise - but they are not necessary and usually aren't included in most designs. Generally we see like 50pF to 100pF when they are used. These capacitors can reduce the effective max length of the bus as well. 

Clemens is also correct on idle fail-safe - we do have an application note that goes into greater detail on how to size these resistors: https://www.ti.com/lit/an/slyt324/slyt324.pdf

These "fail-safe" resistors can also increase the noise margin for devices with Idle fail-safe. 

Please let me know if you have any other questions!

Best,

Parker Dodson

Hi Ali,

Yes this device is open/idle/short fail-safe. 

Above is a section of the datasheet. You can tell if a device is open/idle/short fail-safe if all of the VIT+ (some datasheets will call it VTH+) specs are < 0V - since the max value of VIT+ is -20mV that means when the bus is idle, open circuited, or short circuited the output at the "R" pin will read high. When the bus is idle/shorted/opened the input differential voltage should be about 0V.  

Best,

Parker Dodson