Serial Communications Interface; Rs-485 Serial Communications; Controller Configuration; Sending Commands And Data - Omega CN63100 Series User Manual

SERIAL COMMUNICATIONS INTERFACE

RS-485 Serial Communications

The optional RS-485 serial communication interface provides two-way
communication between the controller and other compatible equipment such
as a printer, PLC, HMI, or a host computer. In multipoint applications, each
controller can be configured with a unique node address ranging from 0-99.
Through this serial interface, data from the controller can be interrogated or
changed, alarm output(s) reset and Auto-tune invoked.
Since the same pair of wires are used for both transmit and receive, only
one-way communication is possible at a time. The controller has a variable
response time, to allow the host device adequate time to release the
communication line after issuing a command to the controller.

Controller Configuration

The controller's serial communication format is configured in Serial
Communication Program Module 6-SC using the front panel. Baud rate and
character frame must be matched to the other communicating device. The node
address parameter is a unique address number assigned to each slave unit on the
bus.

Sending Commands And Data

When sending commands to the controller, a command string of ASCII
characters must be constructed. The string varies in length depending on the
nature of the command. At most, a command string consists of a Controller
(Node) Address number (not required for address of 0), a Command Code
character, a Register Identification character (for most commands),
Numerical Data (if writing data to the controller) and ending with a string
Terminator of "*" or "$". The controller will not respond with an error
message to invalid commands.

Sending Numeric Data

Data written to individual registers must be limited to the registers
numerical data range (See Register Identification Table). If more digits are
sent, the controller only accepts the last four digits of the numeric data.
Negative numbers must have a minus sign. The controller ignores any
decimal point and conforms the number to the register identification
resolution. (Example: "25" is written to the proportional band register. The
value recorded by the register is now 2.5. If a value of 25% is intended, write a
value of 25.0 or 250.

Controller (Node) Address

Code Description
N Controller Node
Address Specifier

Commands Table

Code Description
T Read Value
(Transmit)
V Write Value
(Change)
R Reset Alarm
C Control Action
P Print Block
Request
-57-
Comments
Target a specific controller with the next
Command. Must be followed by a one or two
digit (0-99) controller node address number. Not
required for a node address of 0.
Comments
Read value register command. Must be followed
by Register ID character A-M, BB, HC, or W.
Write value register command. Must be followed
by Register ID character B-H or J-M and
appropriate Numeric Data.
Write alarm register command. Must be followed
by Register ID character G or H.
Write control register command. Must be
followed by Register ID character S-U with
Numeric Data of 1 or 2.
Read block register command. Allows multiple
reads with one command.