I have an older SLC500 that has a PLS card in its rack. I want to remove the SLC and add a L23E-QBFC1. Can a resolver be wired up to the High Speed Counter, or does it have to be an encoder?
No, a resolver produces sine waves, and encoder produces pulses. A resolver is absolute, but a quadrature encoder is not. There will be more to consider for your application that switching sensors and cards. I am a fan of resolvers, and AMCI makes a resolver module for most A/B platforms.