Data Delivery Devices VHF, UHF & ISM Wireless RTU RFScada 8ADI-9DO 4ADI-5DO User Manual

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 81 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
DAQFactory Configuration and Operation. 
 
  DAQFactory is a very powerful process control, monitoring and acquisition program available 
form Azeotech  (http://www.azeotech.com
). Running on a PC DAQFactory comes with built support 
for connecting to an RFScada device, so a complete application may be built very quickly without 
requiring complex details such as Modbus addresses, I/O maps etc.  
Due to the speed of application 
development and the built in drivers PC 
applications connected to an RFScada 
system are possible that would not have 
been economically feasible in the past. 
Data Delivery Devices LLC can provide the 
final application tailored to your 
requirements or the end user may write his 
own application using the developer 
version of DAQFactory.  
  
  This gives an overview of 
configuring DAQFactory for operation with 
the RFScada units, plus accessing all of 
the RFScada status, inputs and outputs 
from within the DAQFactory developer 
version. For full details of DAQFactory 
programming and operation please refer to the DAQFactory manuals. 
 
Verifying Installation. When creating channels in DAQFactory ‘RFScada’ should appear in the 
available device list. If it does not then verify the two files RFScada.dll and RFScada.dds are in the 
main DAQFactory directory and restart DAQFactory.   
 
RFScada Configuration. The RFScada units all need to be correctly configured before operating with 
DAQFactory. There are several modes of operation with many complex routing combinations and 
settings possible. Typically a physically non-existent ‘virtual’ units registers will be overwritten by 
DAQFactory for outputs, and the RFScada master device will then route these overwritten registers to 
appropriate physical outputs. Use the RFScada configuration program to initially setup the RFScada 
devices for required routing. 
 
DAQFactory ‘Device Number’ and 
RFScada ‘Units’. In all DAQFactory 
access and commands the DAQFactory 
‘device number’ corresponds to the 
RFScada physical (or virtual) unit, even if 
the unit is not connected to the PC serial 
port. This is because all RFScada units 
in a system continually exchange data 
via the radio network, with the ‘master’ 
unit, 0, accumulating input data from all 
the slave units then sending output data 
to all the slaves per the preset 
configuration. The ‘master’ RFScada 
unit, which has an assigned unit ID 0 is 
Device 0 in DAQFactory. The slave and 
any ‘virtual’ RFScada units will have ID’s 
of 1 to 31 which are also their Device  
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 82 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
numbers in DAQFactory. When DAQFactory accesses a Device number other than 0 it is actually 
reading or writing to the physical RFScada Unit 0 (master) which is connected to the PC’s serial port; 
RFScada Unit 0 will then read or write data via radio to the requested RFScada unit. All of this 
reading, writing, storing and forwarding occurs inside the RFScada Unit 0, and is completely 
transparent to the user and DAQFactory. For example, to access Unit 7, even though it is not 
physically connected to the PC (and it may be many miles away) in the DAQFactory channel setup 
assign the Device to 7.            
 
Physical Interface. The physical serial port connection from the PC running DAQFactory must be 
made to the RFScada device that is configured as the master, as it is the only device in an RFScada 
network with access to all of the RFScada network registers. The serial port connection may either be 
RS-232 or RS-485 (2 wire hardware automatic). All serial port parameters except the COM port are 
assigned automatically.  
 
DAQFactory Serial Port Selection. Before 
any DAQFactory access to the RFScada 
network is possible the COM port must be 
selected from within DAQFactory. A 
DAQFactory ‘channel command’ may be used 
to do this. First create a DAQFactory channel 
with the following properties, Device Type: 
RFScada; Device Number: 0; I/O Type: 
Command. Now when this channel is set to a 
value from within DAQFactory the value will 
become the serial port used for RFScada 
access. So simply assign a value of 1 to 16 to 
set the connected COM port. Once set the 
COM port is typically never changed, so it may 
easily be set once in the initial startup 
sequence. 
 
DAQFactory Serial Port Status. There are many possible serial port errors that could occur during 
communication between the PC running DAQFactory and the RFScada units, for example the user 
could attempt to select a non existent serial port or the serial cable could be unplugged. The status of 
serial port communications may be monitored from within DAQFactory and of course it may be used 
to initiate alarms and warnings. To access the serial port status set up a channel as Device Type: 
RFScada; Device Number: 0; I/O Type: Special; Channel: 1. Reading the channel will return the serial 
port state, with the following meanings: 
 
0 Correct operation 
1 to 4  Failed to initialize 
5 – 9  Internal initialization errors 
10 - 12  Failed to read correctly 
13 to 16  Failed to write correctly 
 
RFScada Radio Network Status. If there are multiple physical RFScada units in the system then the 
RFScada units will continually communicate amongst themselves via the built in radios. The status of 
this radio network may be monitored from DAQFactory, and of course it may be used to initiate alarms 
and warnings. To access the RFScada radio network status set up a channel as Device Type: 
RFScada; Device Number: 0; I/O Type: Special; Channel: 2. Reading the channel will return the radio 
network status, with the following meanings.  
 
 
0  Correct operation, every unit is communicating correctly.  
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 83 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
1   Some, but not all RFScada ‘slave’ units are responding to radio signals from 
the RFScada ‘master’ unit. 
2  None of the RFScada ‘slave’ units are responding to radio signals from the 
RFScada ‘master’ unit. 
 
If the radio network status is 1 it is possible to find out which units are not operating correctly, refer to 
the RFScada individual network status.  
 
RFScada Individual Network Status. This returns the operational status of an individual RFScada 
unit. To access a units status set up a channel as Device Type: RFScada; Device Number: The units 
ID, 0 to 31; I/O Type: Special; Channel: 0. Reading the channel will return units radio network status. 
0 means the unit is responding correctly, and 1 indicates that there is no response from the unit. 
Typically this status would only be read after an error was reported from reading the RFScada Radio 
Network Status, since it is much easier to read a single summary status than poll each individually.  
 
RFScada Software Version. The software version installed in the RFScada master unit may be read. 
To access the RFScada software version set up a channel as Device Type: RFScada; Device 
Number: 0; I/O Type: Special; Channel: 3. Reading the channel will return the software version as a 
number, e.g. 24 means software version 2.4   
 
Local and Remote Analog Inputs. Analog inputs from every RFScada unit in a system may be read 
using the ‘A to D’ read function. To read an input set up a channel with Device Type: RFScada; 
Device Number: The units ID, 0 to 31; I/O Type: A to D; Channel: the units channel, 1 to 8. Reading 
the channel will return the analog input as a number from 0 to 1023, which corresponds to 0 - 20mA.  
 
Local and Remote Digital Inputs. Digital inputs from every RFScada unit in a system may be read 
using the ‘Dig In’ read function. To read an input set up a channel with Device Type: RFScada; Device 
Number: The units ID, 0 to 31; I/O Type: Dig In; Channel: the units channel, 1 to 8. Reading the 
channel will return the digital input as a number, either 0 for the input open circuit  or 1 if the input is 
shorted.  
 
Local and Remote Analog Outputs. 
Analog outputs on every RFScada unit in a 
system may be written to by ‘overriding’ 
analog inputs that are then routed by the 
RFScada master unit to the desired analog 
output(s). (refer to the rest of this manual for 
a full explanation). Typically a non-existent 
‘virtual’ units analog input is over written, 
and this is then routed wherever it is 
desired. To do this set up a channel that will 
use the ‘D to A’ write function. Use Device 
Type: RFScada; Device Number: The units 
ID, 0 to 31; I/O Type: D to A; Channel: the 
units channel, 1 to 8. Write to the channel a 
value from 0 to 1023, which corresponds to 
0 - 20mA.  
 
Local and Remote Digital Outputs. Digital outputs on every RFScada unit in a system may be 
written to by ‘overriding’ digital inputs that are then routed by the RFScada master unit to the desired 
digital output(s). (refer to the rest of this manual for a full explanation). Typically a non-existent ‘virtual’ 
units digital input is over written, and this is then routed wherever it is desired. To do this set up a 
channel that will use the ‘Dig Out’ write function. Use Device Type: RFScada; Device Number: The  
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 84 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
units ID, 0 to 31; I/O Type: Dig Out; Channel: the units channel, 1 to 8. Write to the channel either a 1 
(relay active, normally open contacts closed) or 0 (relay inactive, normally open contacts open).  
 
Cautions when Writing to Outputs. The RFScada Units are designed for operation in many diverse 
applications, and may control devices such as motors and pumps. It is possible during operation that 
the PC could fail, it may lose power or the serial connection between the PC and the RFScada Unit is 
lost for some reason. If this occurs it is important that the RFScada sets all of its outputs to the default 
‘off’ state, (Analog outputs at 0 mA, all digital output relays off) to prevent any possible hazards or 
equipment damage. For this reason the RFScada Unit has a user programmable ‘Modbus Override 
Time’ value that needs to be set appropriately for the application (the default is 10 seconds). If a 
Modbus write to ‘overwritten’ registers does not occur within this time all overwritten registers on that 
unit will revert to the default state. So, in the DAQFactory application any output writes will need to be 
repeated by DAQFactory within the ‘Modbus Override Time’ to prevent written values reverting to 
default values. Just writing to a single output, either analog or digital, on a unit will reset that units 
timeout and all overwritten values on that unit will remain without requiring any other writes, since the 
timeout is for the unit as a whole and not for individual registers. A simple DAQFactory ‘Sequence’ 
that keeps writing more frequently than the Modbus override time to any register on any overwritten 
Unit will allow correct operation.     
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 85 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990  
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 87 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
Modbus Configuration, Control and Monitoring. 
 
When the RFScada units are shipped they will already be configured for the final application, 
and no further programming, configuration or adjustments are required. Each unit stores its own 
settings inside non volatile memory where they will remain until the unit is reconfigured. Connection to 
power is not required to maintain these settings, there are no batteries or similar volatile devices 
required for storage. 
 
It may, however be necessary to change settings in the field if additional units are added to the 
system or changes in the configured settings are desired. It may also be desirable to monitor and 
possibly control conditions at various units using a computer. The RFScada units have this capability 
built in, via an industry standard protocol called Modbus, and by using a standard PC with suitable 
software virtually every input, output and configuration setting may be monitored or changed in the 
field by the user. It is also possible to permanently store new configuration settings in each unit. 
PC software is available from Data Delivery Devices LLC that allows units to be reconfigured 
in the field. The software also has basic monitoring and control capability, to allow the user to monitor 
or make simple control adjustments in the field, primarily intended for testing and demonstration. The 
complete Modbus map is also included here, so users may also connect to the RFScada devices 
using their own software via applications such as DAQFactory, LabView, Wonderware, Visual Basic 
etc.  
 
Physical Interface. 
The RFScada devices have two types of interface supplied as standard, called RS-232 and 
RS-485. Each interface has its own physical connector, with the RS-232 connector being a 4 pin 
Molex type socket on the lower right hand side of the board marked J15, and the RS-485 connecter is 
a three pin terminal block marked J16. Only one interface may be used at a time, and a 2 pin jumper, 
located by the RS-485 terminal block and marked J1, allows the user to select either RS-232 or RS-
485 operation. Install the jumper block for RS-485 operation, and remove it for RS-232 operation.  
Standard PC’s have an RS-232 serial port (typically a 9 pin male connector, occasionally a 
male 25 pin on the rear of the PC) which connects via a suitable cable to J15 on the RFScada board. 
A suitable cable is available from Data Delivery Devices LLC for connection to a PC’s RS-232 port, or 
use the following table for connections if constructing you own cable.  
 
PC RS-232 to RFScada Interface Connections 
Signal  9 Pin PC Serial Port  25 Pin PC Serial Port  RFScada 
Received Data to PC  Pin 2  Pin 3  J15 Pin 1 
Transmit Data from PC  Pin 3  Pin 2  J15 Pin 2 
Ground  Pin 5  Pin 7  J15 Pin 3 
Shield Ground  Shield  Shield  J15 Pin 4 
 
 
For many industrial environments or locations which require long cable runs a standard called 
RS-485 is often used instead of RS-232, as it is far less prone to interference and many devices may 
be connected in parallel to a single interface cable. Low cost converters and other interface devices, 
such as electrical isolators, are available to allow a PC’s standard RS-232 serial port to convert RS-
232 data to the RS-485 standard. There are several versions of RS-485 available, the RFScada units 
conform to the most popular, called 2 wire since just two wires plus ground are required for 
interconnection. The following table lists the connections.  
 
 
 
 
RS-485 to RFScada Interface Connections  
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 88 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
Signal Connection 
Ground  J16 Pin 3 
A  (transmit & receive)  J16 Pin 1 
B  (transmit & receive)  J16 Pin 2 
 
RS-485 networks often use a terminator resistor, value 120 
Ohm at either end of a transmission line. The RFScada units do not 
have this resistor on the main board, to allow it to be connected at any 
point. If the RFScada unit is the last device on the RS-485 network a 
120 Ohm resistor may be connected between the A & B connections. 
Additionally surge arrestors may be installed on the 8ADI-9DO devices 
as shown if very long cable runs are used. The 4ADI-5DO board 
already has surge arrestors on the printed circuit board. 
As a final precaution when using extreme cable lengths a 100 
Ohm resistor is sometimes installed in series with the shield between 
devices. If a large ground Voltage difference appears between the two sites the resistor prevents 
heavy currents flowing in the shield between locations.   
 
Software Interface. 
Suitable software is required on a PC to communicate with the RFScada devices. Software  
may be downloaded from the Data Delivery Devices website at no charge to provide configuration and 
basic monitoring of the units; this software is actually communicating with the RFScada devices via 
Modbus, using the following commands and Modbus ‘map’. It may be a useful starting point before 
attempting to connect using custom Modbus software; the Data Delivery Devices software may be 
used to verify hardware cables and connections first. 
 
 
 
 
When using Modbus to access the RFScada devices 
care must be taken as it is possible to activate outputs, 
completely alter the operation of individual units, the 
complete system and even render units inoperable until 
re-programmed for the desired operation. If the units are 
remote, for example being accessed via a Modem, it is 
possible to write values that effectively disable remote 
Modbus access. It is recommended that any changes be 
thoroughly tested with all external circuitry disconnected 
to verify correct operation before final connection. 
Remember to write changes to non volatile memory so 
they will remain after power is cycled to the device.   
 
The connection data rate is fixed at 9600 baud, no parity with one stop bit. The units will 
respond to three Modbus commands, command 3 (0x03 hex) which allows the user to read one or 
more registers at once, command 6 (0x06 hex) to write to a single register and command 16 (0x10 
hex) which allows one or more registers to be written at once. Nearly all of the registers may be 
written to, with the exception of a few, such as the software version installed (register 609) which can 
only be read with command 3. To allow easy ‘block writes’ of register areas that may contain a read 
only register no errors will be reported via Modbus for attempted writes to read-only registers; they will 
simply not be written. It is important to understand the method of communication between RFScada 
units, as although all registers are available in every unit only a few are updated in ‘slaves’, whereas 
all registers are updated at the ‘Master’ unit, designated 0. To determine the type of unit read register 
608, if it is zero this unit is the RFScada system ‘master’ and all registers are accessible. Under 
CAUTION 
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 89 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
normal circumstances Modbus access and control would be at unit 0, allowing full access to the 
system. Access at slaves is primarily intended for testing, to change local settings, such as a timeout 
value, or to override and ‘force’ local inputs via Modbus. In the following descriptions it is assumed 
that the Modbus connection is made to the master unit, 0.  
When connected via Modbus to a slave unit (i.e. the units id is 1 to 31) the only registers that 
have significance are the 10 related to that units id (for example 170 to 179 for unit 17, 30 to 39 for 
unit 3 etc), registers 608 to 614 and register 3318.      
 
Register Descriptions: 
The first 320 registers supply present readings and status for the units, with each unit having 
10 registers. The first is the state of the 8 digital input switches, with a zero bit indicating an input 
switch is open. Bit 8, (which cannot be overwritten via Modbus, see explanation later) indicates if this 
unit is correctly communicating with the system master unit. The next 8 registers correspond to the 
user analog inputs, each being a 10 bit resolution input, with 20mA being a full scale reading of 1023. 
0 corresponds to 0.0 mA, so it is possible to tell if a 4-20mA loop device is indicating minimum output 
or if the loop has been broken. The last register is the analog measurement of the DC voltage on the 
RFScada board, and may be used for general indication or for early warning of failing power, for 
example from a solar power supply. It is typically around 18 Volts DC when the unit is operating at 
115 VAC, or about 1 Volt below the DC input Voltage if operating from an external DC power supply. 
Approximately 51 Volts DC is the full scale input for this reading, so values about 340 -380 are normal 
when operating on 115 VAC line input.  
Any of these 320 registers may be forced or ‘overridden’ via Modbus, to override local or 
remote conditions. Outputs on all units that rely on ‘Modbus overridden’ input registers as their signal 
‘source’ will now output signals using these ‘Modbus overwritten’ values as sources. The RFScada 
‘real’ values, taken from external sensors and switches for that relevant unit, will be blocked while 
overwritten via Modbus. All input registers for an overridden unit will be locked, so even if just the 
digital inputs on unit 12 are Modbus overridden all of unit 12’s registers are held at the present state. 
The Modbus overridden values will remain current until Modbus write commands for that particular 
units registers have not occurred for the time specified in the ‘Modbus override time’ register, 613. 
Once the registers have not been overwritten for that time the registers will automatically revert to 
sourcing signals from system read inputs, such as analog inputs and switches. This allows great 
flexibility, as any input on any unit may effectively be overridden via Modbus for testing or control 
purposes. Once Modbus overrides stop the unit will revert to normal operation. Only registers 
associated with ‘Modbus overridden’ ones are affected, and all other operations, including control, 
communications, monitoring and Modbus activity continue to occur normally.  For applications that 
require some outputs to be driven only from Modbus simply configure those outputs to be driven from 
an unused unit ID, then they will only be updated from Modbus.  
The next 128 registers, from 320 to 447, control configuration for all the relay signal sources. 
These registers are similar to one another, and just differ by the relay, the unit and input bit that they 
refer to. Each relay is individually controlled by a digital input (or the Modbus register corresponding to 
that input). For example, register 368 configures relay 1 and 2 on unit 12. The least significant byte 
controls the signal source for relay 1, and the most significant byte relay 2. In each byte the most 
significant 5 bits are the source unit ID for the relay signal, and the least significant 3 bits are the 
digital input bit. So, in this case if the lower byte was 11011010 Binary (218 decimal or 0xDA hex) 
relay 1 in unit 12 would be driven by digital input 3 on unit 27. If the upper byte was 01100111 Binary 
(103 decimal or 0x67 hex) relay 2 in unit 12 would be driven by digital input 8 on unit 12 (its own unit). 
Each relay output may be sourced from any digital input, so it is possible to drive multiple relays on 
multiple units from the same digital input.  
The next 128 registers, from 448 to 575, control configuration for all the analog output signal 
sources. These registers are similar to one another, and just differ by the analog output, the unit and 
analog input channel that they refer to. Each analog output is individually controlled by an analog 
input (or the Modbus register corresponding to that input). For example, register 491 configures 
analog outputs 7 and 8 on unit 10. The least significant byte controls the signal source for analog 
output 7, and the most significant byte analog output 8. In each byte the most significant 5 bits are the  
						

							RFScada 8ADI-9DO/4ADI-5DO Manual Ver 3.6 Copyright ©2005 Data Delivery Devices LLC Page - 90 – Bartlesville OK Tel 918-335-3318      FAX 918-398-9990 
source unit ID for the analog signal, and the least significant 3 bits are the analog input channel. So, 
in this case if the lower byte was 11011010 Binary (218 decimal or 0xDA hex) analog output 7 in unit 
10 would be driven by analog input 3 on unit 27. If the upper byte was 01100111 Binary (103 decimal 
or 0x67 hex) analog output 8 in unit 10 would be driven by analog input 8 on unit 12. Every analog 
output may be sourced from any input, so it is possible to driven multiple (or all) analog outputs from 
the same analog input.  
     The 32 registers from 576 to 607 specify if each unit is enabled. Register 576, for the 
system master (unit 0), must always be enabled, as it control communications between all units. If a 
non existent unit is enabled here the system will not operate, and indicate a ‘network’ error status.   
Register 608 is the ID of this device. If the ID is zero this unit will be the system master, be 
responsible for routing all signals between units, will have virtually all of the configuration settings for 
the system and will control communications between all units. One unit in a system must be the 
master, and there must only be one master in a system. If the ID is 1 to 31 this unit is a ‘slave’ unit, 
and just a few Modbus registers will have significance. Every slave must have a unique ID for correct 
operation, allowing a total of 32 units (one master plus 1 to 31 slaves) to be in one system. Slaves do 
not require sequential ID’s, and slaves may effectively be disabled by ‘un-enabling’ them in the 
masters configuration. The ‘receive data’ LED will flash rapidly on a disabled slave that monitors 
network traffic, but since it is never addressed it will never respond and will not transmit. 
Register 609 contains an image of the output relays on this unit. It is read only. 
Register 610 indicates the current network state, again it is read only. If it is zero the network 
is operating correctly and all configured units are communicating correctly; the ‘system status’ LED 
and relay on this and all other units will be on continuously. If this register contains 1 then this unit (if 
not the master) and the master unit are communicating and operating correctly, but at least one unit 
somewhere on the network is not communicating or operating correctly. On this and all other units 
that are operating the ‘system status’ LED and relay will slowly be toggling on and off, indicating an 
error somewhere in the system. Bit 8 in Modbus registers 0 to 320 and Modbus registers 577 to 607 
may be compared to identify the exact enabled unit (or units) that are not responding. If register 608 
contains 2 then this unit is not communicating with any other unit, and the ‘system status’ LED and 
relay will be off. 
Register 611 contains the user Modbus address for this device. It may be anything from 1 to 
98 or 100 to 255 (default is 0, or off). Note that the RFScada units will also always respond to address 
99 (0x63 Hex), so even if the Modbus address is zero or has accidentally been changed and 
subsequently lost the unit may still be accessed using address 99. The users Modbus ‘silent time’ 
(register 614) will also be ignored when accessed using address 99, see register 614 for details. 
Unless multiple RFScada devices are on the same Modbus network or special silent times are 
required it is suggested that the ‘always enabled’ address of 99 be used.  
Register 612 contains the default ‘loss of communications’ timeout value. For slaves, if valid 
radio communications are not received by this unit within this time frame  the unit will change state to 
indicate ‘lost communications’. All outputs will change to default settings (i.e. off) and the ‘system 
status’ LED and relay will turn off. If this unit is the master this register contains the maximum time 
without receiving valid communications from every unit before changing state to ‘network error’; where 
the  master unit and at least one slave unit are communicating and operating correctly, but at least 
one unit somewhere on the network is not communicating or operating correctly. On this and all other 
units that are still operating all outputs will change to default settings (i.e. off), the ‘system status’ LED 
and relay will slowly be toggling on and off, indicating an error somewhere in the system. The register 
time is in seconds, with the default set at 10, which is suitable for most systems with a few units and 
good communications. If many units are in a system this time may need to be extended to prevent 
network errors, for example caused by power being briefly interrupted on a single unit.               
Register 613 contains the time in seconds before reverting to normal operation after Modbus 
‘override’ writes. If a register is written again via Modbus within this time period it will contain the latest 
‘Modbus overridden’ value; if the timer expires the register will revert to normal, being updated by the 
RFScada inputs. Each time a write occurs to the relevant units registers its timer is restarted. See the 
section on registers 0 to 319 for further details.