Compaq LA36 - Manual (Page 154)

D-6
Interface Information
Buffer Control Description
XON/XOFF (DC1/DC3) When the printer is ready to receive data, it sends the 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 the paper runs out,
the printer sends an NAK code (hex 15).
DTR DTR is a hardware buffer control; that is, the Ready Out signal
on interface cable pin 1 (DTR) is used to control the flow of
data rather than the transmission of a character code. When the
printer is ready to receive data, pin 1 is high. When fewer than
255 (63) bytes of space remain in the buffer (or when the printer
is taken offline), pin 1 is low. The computer must stop
transmitting data within 255 (63) characters of DTR being low,
or information may be lost.