You’ll also have to indicate if your computer sends two stop bits to indicate
the end of a byte, instead of one, the default. These serial interface settings
are described in more detail in your Star LaserPrinter 4111Operations
Manual.
Serial interface:protocol
Finally, inSerialmode yourcomputer will useone of two protocols to ensure
data is sentproperly. Protocol (sometimesalsocalled “handshaking”)means
“who says what when”, and is the way your printer tells your computer it’s
ready to receive data. Your computer and printer communicate by sending
protocol control codes (they’re at the front of the ASCII table).
Some programmers call the XON and XOFFcontrol codes “kiss on and kiss
off’; others call the sameprotocol DC 1and DC3 (fordevice control). Either
way, these codes let your printer run the show, telling the computer when to
start and stop sendingdata. Your printer asks to have data held back when its
memory is nearly full or when it senses an ERROR condition.
DTR (Data Terminal Ready) protocol does the same thing slightly differ-
ently. The printer sends a continuous high-voltage signal over the cable as
long as it can accept data, but drops the voltage to say “whoa” to the
computer.
Look in your computer’s operations manual, in the section dealing with
communications protocols, to see which is best for your system. You can
stickto the printer’sdefaultsifyour computer doesnotusetheDTR, butdoes
use XON/XOFF.
2.2.2 Checking your connections
Your computer and printer may have trouble communicating when you first
introduce them to each other. The quick way to find out if your settings and
printer cable are working is to send your printer a printout from your screen
(CTRL-P with MS-DOS).
When that done you will also have to press the print button on the printer,
which makes the printer advance to a new sheet. No laser printer prints and
ejects a page untilit’stold to feed a form, or untilit has received all the lines
the page can hold.
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