HP 3000 Manuals HP 3000 Manuals
Devices that Communicate Asynchronously
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:
* Terminals
* Personal computers (PCs) in terminal emulation mode.
* Serial printers
* Plotters
* 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.
* Typeaheadfacility, which allows terminal users to enter data
before a read is posted.
* Block mode applications.
* Customized terminal
and printer type filescreated with the workstation configurator
utility.
* Datacommunications and Terminal Controller (DTC) switching
capabilities.
* Powerfail session recoveryfor sessions in character mode (that is,
switched, non-switched, nailed, and non-nailed sessions).
NOTE For more information about these device functionalities, refer to
chapter 9, "Describing Asynchronous Devices."