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How your laser printer communicates
Your computer communicates with the Star LaserPrinter 8111 through either
a parallel cable or one of two kinds of serial cable. The printer’s interjhce,
the link or boundary it shares with your computer, defines whether the printer
will accept characters and commands from your computer one byte or one bit
at a time.
A bit is the smallest unit of computer or printer memory. It has either a low
or high electric charge, which we represent with the digits 0 and 1. Usually
eight adjacent bits are grouped to form a byte. Since a byte normally
represents one character, this string of bits- 01OOOOO1- might represent
the letter A.
The serial interface accepts just one bit at a time from your computer. A
parallel interface can handle a whole byte at once, by moving data bits side-
by-side along separate wires. You choose which interface method you want
to use by selecting it on the operator panel, as explained in your Star
LaserPrinter 8111 Operations Manual.
The Star LaserPrinter 8111 is a computer
The Star LaserPrinter 8111 first maps the characters to be printed into its own
random access memory (RAM). That is, the printer builds a “picture” in its
memory corresponding to the page you want to print. When that’s done the
printer can reproduce the page onto paper on its own, letting your computer
get on with other work.
Your Star LaserPrinter 8111 comes with one megabyte of RAM- the
equivalent of about one million characters. A Star LaserPrinter 8111 option
lets you add a second megabyte of RAM if, say, you need to map full-page
graphics or store more fonts. Accompanying all that RAM is another 5 12
kilobytes of read only memory (ROM), containing a library of internal fonts
and the programs that let the Star LaserPrinter 8111 emulate other printers.
A Motorola 68000 computer chip controls both the memory and the printing
mechanism in the printer, called the print engine. The printer stores a whole
page in RAM before printing it. (If a page is so dense that it overflows
memory-a most unlikely event-the Star LaserPrinter 8111 prints the page
on two sheets.)
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