Fix Acknowledge code

src/PlcMod.h

@@ -102,7 +102,7 @@
 #define	ECHO_MESG_FOC_LIM_CMD	54
 #define	ECHO_MESG_REAL_MOD_CMD	400
 #define	OPN_CLS_CMD	101	//open/close command
-#define	ACK_GEN		531	//acknowledge generic plant alarms
+#define	ACK_GEN		516	//acknowledge generic plant alarms
 #define	ACK_MOD_OFFS		510	//acknowledge modulator alarms (offset)
 //#define	ACK_CMD		102	//acknowledge
 //#define	BEAM_DUMP_CODE	141	//command code for beam dump command