SIMATIC S7-400, DIGITAL INPUT SM 421, POTENTIALLY ISOLATED 16 DI UC 24 - 60V, ALARM, DIAGNOSIS SIMATIC S7-400, DIGITAL INPUT SM 421, POTENTIALLY ISOLATED 16 DI, UC 24 - 60V, ALARM, DIAGNOSIS SIMATIC S7-400 digital module input SM 421, DI 16xUC 24/60 V