Apple 310 manual Binary Communication Protocol

C H A P T E R 3

Communication Channels

Table 3-4	Reserved characters in simple communication protocol (continued)
	ASCII
Character	code	Function
Control-Q	17	Start output (XON). Function only if XON/XOFF flow control
		is in use.
Control-T	20	Status query. Causes the server to produce a one-line message
		that describes what the server is doing.
Return	13	End of line. Translated to the PostScript language newline
		character.
Line-feed	10	End of line. This is the PostScript language newline character.
		If a return and a line-feed are received in sequence, only one
		newline character is passed to the PostScript interpreter.
		When a newline character is written to the standard output

file, it is translated to the two-character sequence: return and line-feed.

The serial and parallel communication handlers perform the special processing of the return and line-feed characters, as described in Table 3-4. This processing is independent of the return and line-feed handling performed by the PostScript interpreter itself. Unlike the processing done at the level of the PostScript interpreter, this processing is done regardless of how the data is to be treated by the interpreter.

With the simple protocol, there is no way to ‘quote’ the reserved characters, that is to pass them through to the PostScript interpreter. Nor is there any way to transmit characters in the 'high ASCII' range (128–255) when using parity settings 0, 1, and 2, which cause the high-order bit of each character to be ignored or used for parity. Therefore, with this protocol, the communication link is not fully transparent. This causes no difficult in normal use, however, since the standard PostScript language character set consists entirely of printable characters. The language itself provides means for encoding arbitrary characters in strings (the ‘\nnn’ escape sequence).

When the server encounters an end-of-file character and the job terminates, the server sends an end-of-file character back to the host. This character marks the end of the data (if any) written to the standard output file while the job was being executed. This enables the application program running on the host computer to synchronize with the server, if this is desired, and to correlate a given output batch with the job that generated it.

Binary Communication Protocol

As an alternate to the simple protocol, the LaserWriter Select 310 printer supports binary protocol for both the serial and parallel channels. Binary protocol allows all character codes to be transmitted as data, but also allows certain characters to be used for specifying control functions, which may be handled asynchronously by the communications driver. These functions include status requests, aborting of jobs, end-of-job markers, and flow control for the serial channel.

50 Communication Protocols