My bipolar stepper motor comes with single-ended encoder, which means it has only A, B and R signals and no complentary A, B, and R\ signals. Can I run it with X20SM1426 or X20SM1436. Any particular tweaks in the software that I need to do to accomplish this?
Yes, you can use a single-ended (asymmetrical) encoder with the X20SM1426 and X20SM1436 stepper motor modules. These modules have the asymmetrical ABR encoder inputs as part of the Technical Data for the module. The module hardware cannot accept symmetrical (A & A\, etc) encoder signals, so an 24V asymmetrical AB(R) encoder is the only type supported by the module.
Link: X20SM1426 - Technical Data B&R Online Help (br-automation.com)
The function model will determine the behavior of the digital inputs with regard to the AB(R) interface.
Link: Function description - ABR interface B&R Online Help (br-automation.com)