Communication Dynamics

C H A P T E R 3

Communication Channels

XON/XOFF Flow Control for PC Communication

To set up the LaserWriter Select 310 printer for serial interface with the IBM PC over the serial port using XON/XOFF ﬂow control at 19200 baud, issue the following MS-DOS commands to your computer:

MODE COM1:19200,N,8,1

MODE LPT1:=COM1:

These commands alone are not sufﬁcient to handle XON/XOFF ﬂow control. Some applications may handle this protocol themselves. Otherwise, you should install a different MS-DOS printer driver to avoid communication problems when printing large documents.

Note

You must issue these commands to your IBM PC whenever the computer is turned on. Alternatively, you may place them in

the AUTOEXEC.BAT ﬁle on your MS-DOS disk. ◆

The LaserWriter Select 310 printer comes from the factory with its serial port conﬁgured for option 68: 8-bit data, no parity, DTR ﬂow control, with 57600 baud. If you need to set up the printer for XON/XOFF communication at 19200 baud, send the following routine to the printer from the host, using either the parallel port, or the serial port at 57600 baud.

serverdict begin 0 exitserver

statusdict begin

9sccbatch 0 eq exch 19200 eq and not

{9 19200 0 setsccbatch} if

end stop

This routine tests the current values of the sccbatch parameters (see Chapter 2), and if they are not set for 19200 baud and option 0, it sets these values using setsccbatch.

Note

These changes are not permanently stored, since the LaserWriter Select 310 printer has no EEROM. They will not persist across power cycles. You should send this sequence each time the printer is turned on or whenever the serial communication parameters have been changed. ◆

Data transmitted by the LaserWriter Select 310 printer, whether it is generated by executing the PostScript language program or by some other spontaneous event such as an error, is logically asynchronous with respect to the data received. This means that the host computer must be prepared to consume data received from the LaserWriter Select 310 printer while waiting to send more data to the printer. If the host computer is not set up to do this, the printer and the host may each wait for the other to consume data, and a deadlock will occur.

54	Communication Dynamics