Centronics | Interfaces |
Protocol description
After
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
0.5microseconds. 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.
Programmer Reference Guide |