| ELECTRICAL
        SPECIFICATIONS | Digital |  IOL = (Low level output current) =
        -20mA
 VOL = (Low level output voltage)< 0.51Vdc
 | 
    
      | Light Source | LED (Light-emitting
        diode) | 
    
      | Operating Voltage (VDC) | 5.1 ±0.1 | 
    
      | Operating Current (Max. mA) | 140 | 
    
      | Differential Output Signals
        (incremental) (TTL) | Two square-wave
        voltage signals, channels A and B, in 90°  quadrature relationship | 
    
      | Reference Mark (TTL level)
 | One square-wave pulse |