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
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
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
The LaserWriter Select 310 printer comes from the factory with its serial port configured for option 68:
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. ◆
Communication Dynamics
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.
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