There are twelve electronics signals from the PC to the printer. Out of these, eight signals are data bits and four signals are control signal.

The control signals are: STROBE#, INIT#, SLCTIN#, AUTO FEED XT#.

All these control signals are active low.

  1. STROBE#: The printer should take data when this signal is Low.
  2. INIT#: When INIT# is low, the printer resets its electronics logic and clear the printer buffer.
  3. SLCTIN#: SLCTIN# is an interface enable signal, when this signal is low, the printer responds to signals from the controller.
  4. AUTO FEED XT#: After printing every line, the printer will provide one line feed automatically if this signal is low. This type of line feed known as hardware line feed.

There are five status signal from the printer to PC, these are ACK#, BUSY, PE, SLCT and ERROR#.

  1. ACK#: Signal is an acknowledgement for STROBE# signal from PC. When active, it indicates that printer has received data sent by the PC and the printer is ready to accept next data byte.
  2. BUSY: When BUSY Signal is high, it indicates that the printer is busy and it cannot receive data. This signal becomes high under any of the following four conditions.
    • On receiving STOBE# active.
    • During printing operations.
    • When the printer is in offline state.
    • When the printer senses some error condition.
  3. PE: When PE signal is high, it indicates that there is no paper in the printer.
  4. SLCT: This signal indicates that printer is selected and logically connected to the PC.
  5. ERROR#: This signal indicates that, there is some error condition in the printer. This signal becomes active under any of the following three reasons.
    • Mechanical fault or electronic fault in the printer.
    • The printer is in offline state.
    • There is no paper in the printer.