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data. These two pins go ON when the printer is ready to accept
data. In the 1 byte mode they go OFF after each character is
received. In the 1 block mode they only go OFF when the
printer’s buffer approaches capacity. In both cases they will
stay OFF if the buffer is too full to accept more data.
H XON/XOFFprotocol
The XON/XOFFprotocolusestheASCII characters(DC1)
and (DC3) (sometimes called XON and XOFF, respectively) to
communicate with the computer. When the printer’s buffer ap-
proaches capacity this printer will send a DC3 (ASCII 19) on
TXD (pin 2) to tell the computer that it must stop sending data.
When the printer is able to receive more data it sends a DC1
(ASCII 17) on TXD. The computer can then send more data
until the printer sends another DC3.
■ ACK protocol
In the ACK protocol, this printer sends an ACK (ASCII 6) on
TXD (pin 2) each time that it is prepared to receive a byte of
data.
Wnlpnmltlwkbml
Ctmcl,t!wu.1
Figure G-1. Typical data byte on the serial interface.