Scope traces for a typical KAT500 serial data interface can be found here - https://www.dropbox.com/scl/fi/ypk0ks16rl03d55ugm4t9/KAT500-signal-levels.pdf?rlkey=7iahis4xp0jnua3c8s577cxjq&dl=0 I can also confirm that KAT500 works just fine when interfaced with a genuine MAX 3232 RS-232 line driver. 73, Andy, k3wyc