The Module may require a Software "Z" command (Initialize) right after power-up before it will respond.   Sometimes modules come up in an undefined state upon power-up.  This state can keep the module from accepting any commands.  As an example, an internal clear could be latched on within the GATE ARRAY.  All Function commands are ignored because of this.  An Initialize (Z) will release this and re-set the module to it's default state.  

Sometimes a hardware "Z" from a switch on the crate controller, does not work properly.  It may bounce or not include strobe pulses (S1 and S2).  Our modules use the timing of the strobe pulses in conjunction with the "Z" line to enable and clock the internal circuitry of the GATE ARRAY to re-set the module properly.