Dascom TALLY MIP480, User Manual

Page: 120 / 138

Interface Information
D-4
Buffer Control
Buffer control is a communication emulation used by the computer terminal and the
printer to secure data transmission between the two devices. The buffer control ensures
that the computer does not send information to the printer faster than the information can
be processed in the printer. By telling the computer when the printer can receive data,
the buffer control prevents the printer’s buffer from overflowing.
This printer offers a choice of two different buffer controls for connection to a variety of
computers: XON/XOFF and DTR. If you computer documentation does not recommend
a particular buffer control, try DTR. The following table describes the buffer control.
NOTE: XON/XOFF is the default setting from the factory.
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) charac-
ters 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
the interface cable. (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, DTR is high. When fewer than 255 (63) bytes
of space remain in the buffer (or when the printer is taken offline),
DTR is low. The computer must stop transmitting data within 255
(63) characters of DTR being low, or information may be lost.