Communications Controllers - DEC VAX 4000 300 Manual

• The R215F expander provides space for up to three RF-series ISEs.
• The B400X expander provides 11 additional Q-bus slots for a system
total of 18 Q-bus slots.
additional RF-series ISEs or up to three ISEs and a tape drive (TF85,
TK70, or TLZ04).
• The B213F expander also provides 11 additional Q-bus slots and
provides space for up to four RF-series ISEs or up to three ISEs
and a TK70 tape drive. Contact your Digital representative for more
information on these and other expander products.

1.2.2.4 Communications Controllers

Besides the console serial line, most systems have additional communica-
tions controllers for connecting additional terminals, and for communicat-
ing with other systems over telephone or network lines. Communications
controllers provide standard interfaces between peripheral devices and the
system. Many communications controllers provide support for multiple
data lines.
The following types of communications controllers are available:
• Asynchronous serial controllers
• Synchronous serial controllers
• DECservers
• Network controllers
Serial controllers transmit data one character at a time. A device at the
transmitting end breaks bytes of data into bits. A device at the receiving
end assembles incoming bits into bytes of data.
Asynchronous Serial Controllers
Asynchronous serial controllers provide low-speed connections between
peripheral devices and the system. Asynchronous communication between
the system and the peripheral depends on recognition of a pattern of start
and stop bits, not on a time interval.
Asynchronous serial controllers may be divided into those without modem
support and those with modem support.
You use serial controllers without modem support to connect additional
terminals and printers to your system. For example, the CXA16 module
provides connections for up to 16 serial lines with no modem support.
The B400X also has space for up to four
System Overview 1–23