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Asynchronous Serial Communications
(ASC) is the term used to describe the specific manner in which
communications occur between a HP 3000 Series 900
computer and some of its associated devices. Asynchronous refers
to the protocol used to inform the receiving end of a communications
link that data is being sent and when the data transmission has
completed. Each character is preceded by a special bit, called a
start bit, which signals its arrival. The character is then followed by at least
one stop bit, (a second special bit) that signals transmission of
that character is complete. The types of devices that communicate asynchronously include
the following: Personal computers (PCs) in terminal emulation mode. Modems and other devices that use modem signals. HP PowerTrust UPSs (Uninterruptible Power Supplies)
(herein referred to as UPSs). This asynchronous communication scheme supports the following
device functionality:
Device control capabilities provided
through the FCONTROL
and FDEVICECONTROL
file system intrinsics. Typeahead
facility, which allows terminal users to enter data before a read
is posted. Customized terminal and printer type files
created with the workstation configurator utility. Datacommunications and Terminal Controller (DTC)
switching capabilities. Powerfail session recovery
for sessions in character mode (that is, switched, non-switched,
nailed, and non-nailed sessions).
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