105U-G Wireless Gateway
User Manual
Page
51
©
August 2003
All of the registers between 0 and 49 have a sensitivity value of 1000. If register 34 has
changed value by more than 1000 since the last transmission for that register, then a change
trigger will occur for register 34. Sensitivity values are in decimal and can vary between 1
and 65535 (16-bit).
Up to 50 blocks of sensitivities can be configured. If a register is included in more than one
block, then the first sensitivity value configured will be accepted and later values ignored.
Registers which are not included in any block use the “default” sensitivity which is also user-
configurable. In the above example, the default sensitivity is 1 and is the sensitivity for all
I/O registers not included in the three blocks.
Important Note.
Sensitivity values need to be selected carefully for
analogue or counting
registers as small values can result in a large number of change messages which can overload
the radio channel. A sensitivity value of 1 in 65535 is a change of 0.0015%. If the host
device writes an analogue value to a 105G every 100msec, it will change by at least 1 bit
each time. A small sensitivity value will cause a change message to be sent every 100msec.
If there are many analogue values in the same situation, then there would be many change
messages every 100msec. Sensitivity values for analogue I/O should be set to be greater than
the normal process noise of the signal. For example, if a flow signal has a normal process
oscillation of 2.5%, then the sensitivity should be set to 3% (or a value of 2000) to avoid
change transmissions from the process oscillations.
4.6
Data Bus Configuration - MODBUS
The 105U-G-MD1 module provides interface for Modbus Slave, Modbus Master and Allen-
Bradley DF1. This Modbus interface uses the Modbus RTU protocol - also known as the
Modbus Binary protocol. This manual assumes that the reader has a good understanding of
the Modbus or DF1 protocol.
4.5.2
MODBUS Slave
If you use the 105G Modbus Slave interface, then the host device will be a Modbus Master
device.
The only configuration required for the Modbus slave interface is selecting the Modbus
address and serial port parameters. This is done in the “Serial Settings” screen. A valid
Modbus slave address is 1 to 255.
Each I/O register (and status register) in the 105G can act as one of the following types of
Modbus registers
00001-09999 = Output Coils (digital/binary)
10001-19999 = Input Bits (digital/binary)
30001-39999 = Input Registers (16 bit)
40001-49999 = Output Registers (16 bit)
For example:
•
If the Modbus Master sends the 105G a “read” command for Modbus input 10457, then
the 105G will respond with the value in I/O register 457.
