Chapter 16 PLC Function ApplicationsMS300 
689 
 
16-5-2 Introduction to special relay functions (special M) 
R/W column: RO means read only; RW means read and write. 
Monitors N.O. contact (contact A). N.O. while RUN, contact A. This contact is ON 
while in the RUN state. 
Monitors N.C. contact (contact B). N.C. while RUN, contact B. This contact is OFF 
while in the RUN state. 
Initiates a forward pulse (the instant RUN is ON). Initial pulse, contact A. Produces 
a forward pulse when RUN begins; pulse width = scan cycle. 
Initiates a reverse pulse (the instant RUN is OFF). Initial pulse, contact A. Produces 
a reverse pulse when RUN ends; pulse width = scan cycle. 
Drive malfunction instructions   
Drive direction FWD(0) / REV(1) 
10 ms clock pulse, 5 ms ON / 5 ms OFF. 
100 ms clock pulse, 50 ms ON / 50 ms OFF. 
1 sec. clock pulse, 0.5 s ON / 0.5 s OFF 
1 min. clock pulse, 30 s ON / 30 s OFF 
Frequency reached (when used with M1025) 
Parameter read/write error   
Parameter write successful   
Drive frequency = set frequency (ON)   
Drive frequency = 0 (OFF) 
Drive operating direction    FWD (OFF) / REV (ON) 
Hardware power (Servo On) 
Lock frequency (lock, frequency locked at the current operating frequency) 
Hardware already has power (Servo On Ready)