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INTERFACE INFORMATION
D-8
Serial Protocols
A protocol is a set of instructions that control the way data is transmit-
ted between devices such as a computer and printer. The protocol
ensures that the computer does not send information to the printer
faster than the information can be processed. By telling the computer
when the printer can receive data, the protocol prevents the printer's
buffer from overflowing.
This printer offers a choice of four different protocols for connection to
a variety of computers: XON/XOFF, DTR, RC, and ETX/ACK. If you
computer documentation does not recommend a particular protocol,
try DTR. The following table describes the three protocols.
Protocol
XON/XOFF
When the printer is ready to receive data, it sends the
(DC1/DC3)
XON (DC1) code (hex 11). When fewer than 255 bytes
of space remain in the buffer (or when the printer is
taken offline), the printer sends the XOFF (DC3) code
(hex 13). (When the input buffer is configured for 256
bytes, the buffer limit is reduced from 255 bytes to 63
bytes.) The computer must stop transmitting data
within 255 (63) characters of receiving the XOFF code,
or information may be lost. If paper runs out, the
printer sends an NAK code (hex 15).
DTR
DTR is a hardware protocol; that is, the DTR signal on
interface cable pin 20 is used to control the flow of
data rather than transmission of a character code.
When the printer is ready to receive data, pin 20 is
high. When fewer than 255 (63) bytes of space remain
in the buffer (or when the printer is taken offline), pin
20 is low. The computer must stop transmitting data
within 255 (63) characters of DTR being low, or
information may be lost.
RC
The RC protocol is the same as the DTR protocol,
except that the Reverse Channel signal (pin 11) is used
instead of the Data Terminal Ready signal (pin 20).
Description
User's Manual
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