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3.1.1
ESTABLISHING A COMMUNICATION LINK
North Star HSIO-4
To establish a communication link between two
electronic devices (such as a computer and a
terminal), the operating characteristics of
both devices must be compatible.
The HSIO-4 has four serial I/O ports.
I/O port provides the interface necessary to
establish a communication link between a
HORIZON computer and another electronic device
with a compatible serial I/O port.
RS-232 OR 20mA CURRENT LOOP SIGNALS
Most computers, terminals, and printers use
RS-232 signals. A few commercially used
terminals, such as teletypes, use 20mA
current loop signals.
As supplied, each HSIO-4 port is wired to
use RS-232 signals. 20mA current loop signals
can be accomodated with a configuration
change. Refer to section 3.2.5 for specific
instructions.
ASYNCHRONOUS OR SYNCHRONOUS TRANSMISSION
Each port on the HSIO-4 allows two different
types of data transmission: asynchronous and
synchronous.
Typical communication between a
computer and a terminal is asynchronous.
Synchronous communication is used primarily to
facilitate high-speed computer-to-computer
data transmission.
ASYNCHRONOUS
See Section 3.2 for specific configuration
and programming instructions. As supplied,
each port on the HSIO-4 is configured for
asynchronous operation.
SYNCHRONOUS
To operate an I/O port in synchronous mode,
you must wire the Configuration Header and
the Clock Header, and then program the I/O
port according to the specific procedures in
Section 3.3.
15
Each
User/Technical Manual
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