User guide

Printer Communication Interfaces

A.4 Automatic Port Selection

When the Communication Port Selection feature is set to ‘‘automatic’’ (for

the LA75 Plus and the LA310 MultiPrinter) or to ‘‘shared’’ (for the LA600

MultiPrinter) during setup, either the serial or parallel port automatically

becomes active when valid data is received on it. In the case of the serial port,

valid data means data without a parity error.

At completion of the automatic power-up self-test, both the serial and parallel

ports are disabled. Communication then takes place according to the following

rules:

• Communication on the serial port is enabled by any of the following events,

after which it enters the standby state:

– XON is sent by the printer, if XON/XOFF (or XON/XOFF + DTR for the

LA600) control is selected.

– If DEC PPL2 protocol is selected, the Answerback message (when auto-

answerback is enabled in setup) and then the power-up initialization

message (when enabled in setup) are sent.

– The DTR signal is set high by the printer.

• Communication on the parallel port is enabled by any of the following

events, after which it enters the standby state:

– An ACKNLG (pin 10) pulse is sent.

– BUSY (pin 11) is set low.

– SLCT (pin 13) is set high.

• When one port becomes active, data ﬂow on the other port is disabled. This

control is achieved as follows:

– When the parallel port becomes active, an XOFF code is sent from

the serial port (if XON/XOFF control is enabled during setup, or

XON/XOFF + DTR for the LA600 printer) and the DTR signal is set

low. As long as the parallel port is active, the DTR signal remains low

and data ﬂow on the serial port is inhibited.

– When the serial port becomes active, the parallel port is disabled by

setting the following signals :

ACKNLG (pin 10) is set high

BUSY (pin 11) is set high

SLCT (pin 13) is set low

Printer Communication Interfaces A–5