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• Transmit timing of X-on signal
The X-on signal is transmitted when the power is first
turned on, or when the vacant area in the buffer is
greater than the specified value (typically 512 bytes;
refer to your printer manual).
Figure 3. X-on/X-off thing
X-ON
X-OFF
X-ON
POWER ON Buffer capacity less
than specified value
Buffer capacity greater
than specified value
DTR protocol
Under this system, when the printer is turned on the
DTR enters the SPACE state, meaning that data entry is
enabled. When the rate of data reception is greater than
that of printing, the buffer gradually fills up. Once the
vacant area in the buffer drops below the specified value
(typically 256 bytes; refer to your printer manual), the
DTR sets the status flag to prohibit further data entry.
This flag is output through the DTR pin (No. 20) at
RS-232D signal levels, and through the TTY-TXD pin
(No. 17) at Current Loop Levels.
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