. Data Terminal Equipment (DTE) —Any device
that can transmit or send data; for example, a computer.
. EIA —Electronics Industry Association.
l External Function (EF) data —The purpose of
the EF function is to transfer command information by
using the appropriate control signals from the
transmitting computer to the receiving device. The
word size and bit format of the EF data will be specified
by the appropriate system design data or the individual
equipment specifications.
. External Interrupt (EI) data —The purpose of the
EI function is to transfer status information by using the
appropriate control signals from a transmitting device
to the receiving computer. The word size and bit format
of the EI data will be specified by the appropriate
system design data or the individual equipment
specifications.
l Gateway —A device that serves as a shared entry
point from a local area network into a larger information
resource such as a mainframe computer.
l Handshaking —Signals necessary for complet-
ing I/O operations.
l Hub —Repeats the signal on the cable.
. IEEE —Institute for Electrical and Electronics
Engineers.
o Input —Input refers to input to the computer.
l Input/Output (I/O) word —The I/O word is
defined as a digital word of a specified number of bits,
which has been agreed upon as the basic unit of
communication between interconnected units.
l Input Data (ID) —The purpose of the ID function
is to receive information using the appropriate control
signals from a transmitting device by the receiving
computer. The word size and bit format of the ID data
will be specified by the appropriate system design data
or the individual equipment specifications.
. IOA —Input/output adapter.
. IOC —Input/output controller.
l Output —Output refers to output from the
computer.
l Output Data (OD) —The purpose of the OD
function is to transfer information using the appropriate
control signals from a transmitting computer to the
receiving device. The word size and bit format of the
7-2
OD will be specified by the appropriate system design
data or the individual equipment specifications.
l Protocol —In a computer, protocol is the
procedure required to initiate and maintain operations.
For example, I/O operations of a parallel format use a
request and an acknowledge protocol to perform input
and/or output operations for the transfer of information
between the computer and external equipment.
l RS —Recommended Standard.
l Sink —The sink is defined as that end of a
channel that receives information frames.
c Source —The end of a channel that transmits
information frames.
TOPIC 2—INPUT/OUTPUT (I/O)
ORGANIZATION
All computers are capable of I/O operations. Some
computers rely on the CPU to handle all operations
including the I/O operations. These computers simply
use the circuits in the CPU to handle the I/O operations.
However, the majority of computers use an I/O
processor (fig. 7-1) that enhances the capabilities of the
computer and relieves the burden of I/O processing
from being on the CPU. This allows the computer to
perform other operations while still performing I/O
operations. In this topic we discuss I/O operations in
general terms, using an I/O processor. This includes the
physical aspects, data arrangement, format,
instructions, operations (modes of operation, timing,
Figure 7-1.—I/O processor in a computer system.
