Printer User Manual

Centronics Interfaces
Programmer Reference Guide U26169-J-Z716-1-7600
© Siemens Nixdorf Informationssysteme AG 1995 Pfad: D:\SNI\Mackwitz\u26169\o26169e\26169e.k11
Protocol description
After power-on, the PE signal goes to zero. The SELECT signal and the FAULT signal
become one.
Timing
The host sets the data lines (DATA 1 - DATA 8) according to the character to be transferred.
After a timeout of 0.5 microseconds the host sends a STROBE pulse with a length of at least
0.5 microseconds. The character is stored in the printer buffer and the printer sends a BUSY
signal to the host. When the data byte is stored completely in the printer buffer, the printer
sends a BUSY and an ACKN signal to the host.
The ACKN signal informs the host that a data byte has been received and that the printer is
ready to receive another character.
When the printer buffer is full, the BUSY signal is not reset to stop the data stream from the
host. The BUSY signal is reset only when at least 256 bytes are free in the printer buffer.
When the Stop button is pressed, the BUSY signal remains one and the ACKN signal is not
sent.
If at least 256 bytes are free in the printer buffer, pressing the Start button causes the BUSY
signal to be reset and an ACKN signal to be sent to the host.