8
FX-300-ISE Module Description
2.44 RS485 Modbus
The address (P02) must be unique in the network; two units are not allowed to have the same
address. In a network with the FX-300- DAT as master, all addresses must be assigned without
leaving any address out; i.e. if 3 units are connected to a FX-300-DAT, the addresses 1, 2 & 3 must
be assigned to the three units. The order of the addresses is of no importance. In a network with an
FX-300- DAT, up to 14 slaves may be connected, allowing addresses 1..14.
In a SCADA system
Since different SCADA systems may have different restrictions only the general are mentioned here:
The baud rate (P14)
must be set to the baud rate of the SCADA system.
The address (P02)
must be
unique in the network; Two units are not allowed to have the same address.
Modbus Scaling
The scaling for the ISE output is per parameter no. 9 (low, mid or high) that may differ from the 0/4-20
mA analog output scaling.
Modbus
The FX-300-ISE contains 2 measurements (ISE/mV and temperature). Access to these are gained
through the function code
Read_Input_Registers (04)
. The FX-300-ISE gives access to different
diagnostic values via
Diagnostics (08)
, as shown below.
Read_Input_Registers
Function code
Start address
Number of values
04
1
1 or 2
Value 1 is ISE ppm and value 2 is temperature. The measurements are transmitted in sequence; If
2 values are chosen both ISE ppm and temperature are transmitted. If the value for temperature is
wanted, 2 values must be requested. Both values are rated to 0- 1000 corresponding to the range, but
the temperature has an offset of 1024; i.e. 0-999 ppm is transmitted as 0-1000 and 0-150°C as 1024-
2024. The start address is of no importance but rather only that the number of values determines the
returned values.
Diagnostics
Function code
Sub code (HEX)
Description
08
00
Return Query Data
0A
Clear counters and diagnostics register
0B
Return Bus Message count
0C
Return Bus Communication Error count
0D
Return Exception Error count
0E
Return Slave Message count
0F
Return Slave No Response count
12
Return Bus Character Overrun count
2 Introduction
