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Most MS-DOS and AT-compatible computers support up to three parallel
and two serial ports, which come on expansion boards you plug into your
computer. When you installsuch boardsyoumustsetswitches toindicatethe
number and addresses ofthese ports. Ifyou specify the wrong addresses, you
won’t be able to print.
Serial interface: rate
If you ask for the Serial interface you’ll have to tell your printer more about
how the data will be coming in — in particular its rate and unit size and the
meanings of any special bits.
The Rate parameter specifies how fast data will be arriving, measured in
baud (named after the French communications engineer Jean Baudot). Pick
any of the following data transfer rates:
300 baud
600 baud
1200 baud
2400 baud
4800 baud
9600 baud (the default)
19200 baud
38400 baud.
Roughly,one character a second works outto 11baud. If you’renotsurehow
fast your computer will transmit, the general rule is to experiment. Try
sending a page to print at the highest speed, and work your way down until
the printer’s output looks OK.
Serial interface: special bits
In Serial mode you’ll also have to specify if your computer sends data bits
in groups of seven (most computers send eight, the default for a byte).
Sometimes an extra bit gets appended to make the sum of all bits in each
character always odd or even; that’s calledparity. A parity bit can help spot
transmission errors. If your computer sendsthat extra parity bit, you’ll have
to say whether itproduces anevenorodd numberof“on” bits inthecharacter.
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