C H A P T E R 3
Communication Channels
Unlike the serial port, the Centronics parallel input allows no parameters. It always accepts 8-bit data with no parity, and it reserves the same set of characters for communi- cation functions that the serial port reserves, with the exception of XON/XOFF characters, which are passed through the PostScript interpreter, since flow control is maintained by means of the /BUSY signal.
The Centronics parallel interface is essentially an input-only channel. This means it basically transfers information from the host to the printer. However, the PostScript interpreter always deals with both the input and output sides of an I/O channel.
When operating in Centronics parallel input mode, the printer sets up the 8-pin serial port for the PostScript language print operator. The output from this port may be ignored for simple one-way communication. However, important information may be output via this port. Printer errors are always reported, since the Paper Error signal on the Centronics interface cannot be relied upon to report all printer errors. Table 3-6 summarizes the settings for the serial communications port when it is used as the output port during parallel communication.
Table 3-6Settings for the serial output channel during parallel communication
Parameter | Settings |
Data bits | 8 |
Parity | None |
Stop bits | 1 |
Flow control | DTR |
Baud rate | 9600 |
Protocol | Binary |
Serial Interface
You may also use the serial port as an alternative means of communicating with the IBM PC, using either DTR or XON/XOFF flow control. DTR flow control is preferred, since this is the default serial flow control for the LaserWriter Select 310 printer.
DTR 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 DTR flow control, issue the following MS-DOS commands to your computer:
MODE COM1:19200,N,8,1,P
MODE LPT1:=COM1:
Communicating with an IBM PC | 53 |