Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90051)

Chapter 9 183
Describing Asynchronous Devices
How Connections Set Characteristics
Only full-duplex asynchronous modems are supported for use with
HP 3000 Series 900 computers. Twenty-five pin RS-232-C cables must
be used on each end of a modem connection because, in addition to send,
receive, and ground signals, control signals are also required to control
the modems.
Both terminals and serial printers are supported over modems.
However, because data is traveling for long distances through telephone
lines of varying quality, parity must be used to detect transmission
errors. This means that only printers that support printer-type 21
should be used over modems, since parity cannot be used with other
printer type files.
Theoretically, remote devices are supported at the same speeds as
devices connected directly. However, most full duplex asynchronous
modems support only a limited set of speeds. Common modem speeds
are 300, 1200, and 2400 bps. Note that the device, the modems, and the
data communications configuration must be set to the same
transmission speed for the connection to work.