4-4
4.1.4 MODBUS BTU Protocol
(Optional).
MODBUS is a protocol developed by Modicon
Inc. for communication between programmable
controllers and operator stations which support
them. For a complete description of the
MODBUS interface, request BLH technical
document TD-075. If the MODBUS option is
installed and enabled (DIP switch position 8 =
OFF), interface parameters must be selected
using the DIP switch configurations shown in
Figure 4-2
If the MODBUS option is installed but not
enabled, DIP switch selections will function as
shown in Tables 4-1 and 4-2 (page 4-1).
MODBUS protocol formats are presented on the
following pages.
Figure 4-2. DIP Switch Selections for MODBUS Protocol.
MODBUS FUNCTIONS SUPPORTED:
02 Read Input Status
03 Read Holding Registers
06 Preset Single Register
16 (10 Hex) Preset Multiple Registers
DATA FORMATS:
FORMAT #1: One 16 bit signed integer -
32768 to 32767 for all data
FORMAT #2: Two 16 bit signed integers
for weight data (the two integers must
be added together to get -65536 to
65534) One 16 bit unsigned integer for
status & setup parameters
FORMAT #3: Two 16 bit signed Integers
for weight data (the high word, 1st
integer, must be multiplied by 32768.0
then added to the low word, 2nd Integer)
One 16 bit unsigned integer for status &
setup parameters