6 Outputs
6.1 Modbus‚ Implementation
Integra 1540 offers the option of a RS 485 communication module for direct connection to
SCADA systems using the Modbus‚ RTU protocol. The Modbus‚ protocol establishes the format
for the master's query by placing into it the device address, a function code defining the
requested action, any data to be sent, and an error checking field. The slave's response message
is also constructed using Modbus protocol. It contains fields confirming the action taken, any
data to be returned, and an error-checking field. If an error occurred in receipt of the message,
or if the slave is unable to perform the requested action, the slave will construct an error
message and send it as its response.
The electrical interface is 2-wire RS 485, via 3 screw terminals. Connection should be made
using twisted pair screened cable (Typically 22 gauge Belden 8761 or equivalent). All "A" and "B"
connections are daisy chained together. The screens should also be connected to the “Gnd”
terminal. To avoid the possibility of loop currents, an Earth connection should be made at one
point on the network. See the connection diagram for details.
Line topology may or may not require terminating loads depending on the type and length of
cable used. Loop (ring) topology does not require any termination load.
The impedance of the termination load should match the impedance of the cable and be at both
ends of the line. The Belden 8761 cable should be terminated at each end with a 120 ohm (0.25
Watt min.) resistor.
A total maximum length of 3900 feet (1200 metres) is allowed for the RS 485 network. A
maximum of 32 electrical nodes can be connected, including the controller.
The address of each Integra 1540 can be set to any value between 1 and 247. Broadcast mode
(address 0) is not supported.
The maximum latency time of an Integra 1540 is 150ms (400ms JIS version) i.e. this is the
amount of time that can pass before the first response character is output. The supervisory
programme must allow this period of time to elapse before assuming that the Integra 1540 is
not going to respond.
The format for each byte in RTU mode is:
Coding System:
8-bit binary, hexadecimal 0-9, A-F
2 hexadecimal characters contained in each 8-bit field of the message
Data Format:
4 bytes (32 bits) per parameter.
Floating point format ( to IEEE 754)
Most significant byte first (Alternative – least significant byte first)
see address 21.
Error Check Field:
2 byte Cyclical Redundancy Check (CRC)
Bits per Byte:
1 start bit
8 data bits, least significant bit sent first
1 bit for even/odd parity
1 stop bit if parity is used; 1 or 2 bits if no parity
Data Transmission speed is selectable between 2400, 4800, 9600, 19200 bps.
All settings are user configurable via the set-up screens.
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