Handshaking protocol
X-on/X-off Protocol
X-on/X-off protocol is a system in which the printer transmits a code to the computer to indicate that it cannot accept more data, and a second code when it is once again ready. This protocol can be performed under either RS-232D, RS-422A, or 20-mA Current-Loop signal levels.
The C82307* /C82308* interface card sends an X-on (11H) code when it is ready to receive data, and an X-off (13H) when it is busy. The X-on/X-off signals may be transmitted from the TXD terminal (pin No. 2) at RS-232D signal levels, through the SDA and SDB terminals (pin No. 9, 10) at RS-422A signal levels, or through the TTY-TXD terminal (pin No. 17) at 20-mA Current-Loop signal levels.
After the X-on flag has been set, data can be accepted up to the maximum capacity of the buffer.
•Transmit timing of the X-off signal
The X-off signal is transmitted when the vacant area for bytes in the buffer drops to flag set level.
•Data transfer after X-off signal
Data can be sent to the printer even after the X-off signal is transmitted as long as sufficient room for data remains in the buffer. However, if the transmitted data exceeds the vacant area in the buffer, it will be discarded. The X-off character will be transmitted again when the remaining buffer capacity is actually 0 bytes. At that time, a BS code (08H) and "/" character (2FH) will be sent to the printer.