Frequency limit setting is Not available under DC-
INT, AC+DC-EXT, AC-EXT, AC+DC-Sync and AC-
Sync output modes. 
  Before change freq limit setting, if FREQ setting 
value is bigger than desire freq limit value, the freq 
limit value cannot be change accordingly. 
  The range of frequency limit will be limited within 
the certain minimum value in accordance with the 
output frequency setting. 
  There are 2 sets of frequency limits in total.