BusWorks® Model 989EN U
ser’s Manual Modbus TCP/IP Digital I/O & Counters
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Acromag, Inc. Tel:248-295-0880 Fax:248-624-9234 Email:
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DNS refers to the Domain Name System or Domain Name Server. This
refers to the system used to associate an alphanumeric character string with
a numeric IP address. The DNS is actually a distributed database of domain
names and corresponding IP addresses. These servers contain information
on some segment of the domain name space and make this information
available to clients called
resolvers
. For example, the DNS allows us to use
“Acromag.com” as an IP address rather than a complicated number string.
Modbus registers are organized into reference types identified by the leading
number of the reference address:
Reference
Description
0xxxx
Read/Write Discrete Outputs or Coils. A 0x reference
address is used to drive output data to a digital output
channel.
1xxxx
Read Discrete Inputs. The ON/OFF status of a 1x
reference address is controlled by the corresponding
digital input channel.
3xxxx
Read Input Registers. A 3x reference register contains a
16-bit number received from an external source
—e.g. an
analog signal.
4xxxx
Read/Write Output or Holding Registers. A 4x register is
used to store 16-bits of numerical data (binary or decimal),
or to send the data from the CPU to an output channel.
Note:
The ON/OFF state of discrete inputs and outputs is represented by a
1 or 0 value assigned to an individual bit in a 16-bit data word (port).
This is sixteen 0x or 1x references per data word. With respect to
mapping, the lsb of the word maps to the lowest numbered channel of
a port and channel numbers increase sequentially as you move
towards the msb.
All I/O values are accessed via the 16-bit Input Registers or 16-bit Holding
Registers given in the Register Map. Input registers contain information that
is read-only. For example, the current input value read from a channel, or
the states of a group of digital inputs. Holding registers contain read/write
information that may be configuration data or output data. For example, the
high limit value of an alarm function operating at an input, or an output value
for an output channel.
Each 989EN unit has a default factory configuration as noted in the
Specifications section. Your application will likely differ from the default
configuration provided and the unit will need to be reconfigured. You may
reconfigure most features of this unit by issuing the appropriate Modbus
functions to Register Map registers, as required by your application. You
may also use a standard web browser to access the built-in web pages of
the unit to perform basic I/O & reconfiguration.
ABOUT MODBUS
TCP/IP
Domain Name System
(DNS)
MODBUS
REGISTERS
The “x” following the leading
character represents a four-
digit address location in user
data memory.
The leading character is
generally implied by the
function code and omitted from
the address specifier for a
given function. The leading
character also identifies the
I/O data type.
Register Functions