Specifications
COMMUNICATIONS
The D3000/4000 is designed to be easy to interface to
all popular computers and terminals. All communications
to and from the module are performed with printable
ASCII characters. This allows the information to be
processed with string functions common to most high-
level languages such as BASIC. For computers that
support standard interfaces such as RS-232C, no
special machine language software drivers are neces-
sary for operation. The ASCII format makes system
debugging easy with a dumb terminal.
RS-232C is the most widely used communications
standard for information transfer between computing
equipment. RS-232C versions of the D3000/4000 will
interface to virtually any computer without additional
hardware. RS-232C is not designed to be used as a
multiparty system; however the D3000/4000 modules
can be daisy-chained, as shown in Figure 3, to allow
many modules to be connected to a single communica-
Figure 3. RS-232 Daisy Chain Network.
tions port. In this network, any characters transmitted by
the host are received by each module in the chain and
passed on to the next station until the information is
echoed back to the host. In this way all commands given
signal to handle as many as 32 more drivers allowing
you to extend the RS-485 network by adding a repeater
every 30 channels. The A1000 converter also provides a
power supply output of +24V @ 1A to power the mod-
ules. The supply protects against overloads and short
circuits. To protect the host computer, the host input con-
nection is optically isolated to 1500Vac, and the RS-485
output connections are tied to ground to provide a safe
path for static discharge.
Scaling data in RPM
A D4000 voltage output module is used to supply the
control signal to a motor speed controller. The full scale
range of the D4000 is 0 to +10V. When this voltage is
applied to the motor, speed varies from 100 to 3000
RPM. To command the motor to turn at a specified RPM
requires some computation to obtain the correct com-
mand data.
APPLICATIONS
100 Channel Network
Figure 5 shows 100 analog outputs being controlled by a
personal computer and D4000 modules. RS-485 is the
obvious choice for high channel count networks because
of its multidrop capability.
RS-485 is inherently half-duplex so it cannot transmit and
receive at the same time. Each module contains its own
unique channel address that you specify. Only the chan-
nel requested will respond to your command. The mod-
ules work on a command/response protocol so they can
never initiate a transmission sequence. Therefore, errors
due to bus contention are eliminated.
Since very few computers or terminals have built-in sup-
port for RS-485, a DGH A1000 RS-232C/RS-485 Con-
verter is required. RS-485 handles only 32 drivers on
each communications port. The DGH A1000 acting as an
RS-485 Repeater reshapes and amplifies the RS-485
Figure 5a. 100 Channel Network.