Detcon RXT-320 - Manual (Page 26)

RXT-320 Wireless Modbus ™
RXT-320 Wireless IM Rev. 2.1 Page 22 of 27
4.2.3 Register – 4-20mA Reading
There are two 4-20mA inputs and their current value is stored in the 4-20mA A and B registers. The value of
these register will range between 0 to 2048 with 0 being 0mA and 2048 being 20.48mA. Therefore a 4mA
input will read 400 and a 20mA input will read 2000. Any currents above 20.48mA will remain at 2048 since
this is the maximum value for this register.
4.2.4 Register – Battery Info
If a Detcon battery pack is connected to the RXT-320 transceiver, there are five registers associated with
information about that battery. The RXT-320 utilizes the I2C interface to read battery status and only one
Detcon battery pack can be read per RXT-320.
The controller can determine if a battery is present by reading the Status Register (register 8204). There are
two bits in this sixteen bit register pertaining to the battery, Battery Detect – bit 6 (lowest bit is 0) and Battery
Fault – bit 7. Both bits default to a value of 0. Battery Detect will be set once the first read of the battery over
the I
2 C interface was successful. Battery Fault will be set if a battery was detected but the last read failed.
Battery Fault is re-evaluated upon every read of the battery which is set to approximately every 5 seconds.
Register 8206 (I
2
C Batt Read Fails) will increment by 4 each time there is a failure since there are 4 attempts
before declaring failure. This register can be cleared by writing a 0 to it at any point.
Once the battery has been detected the controller can read the battery life (registers 8199 and 8200). The
battery adjusts these values based upon the average current usage. If this usage varies widely over time it will
take some time to re-adjust the battery life readings. For instance an Alarm Station with no alarms will
consume a very small amount of battery but when Alarms are active this will jump to a much higher level of
usage. So in this case battery life may go from several weeks down to several hours.
The battery life is presented in two forms, life remaining in percentage (register 8199) and life remaining in
minutes (register 8200). The battery Life remaining is percentage is a value between 0 and 100 and battery life
in minutes is an unsigned value between 0 and 65535. Both readings are generally necessary to provide
appropriate feedback to the user. Life in minutes is the best for determining when to change the battery. For
example if the user wanted to be notified a day before the battery needed to be changed, the user could set a
threshold in the controller to be notified of low battery after 1440 minutes (1 day).
Since 65535 is the maximum value for life remaining in minutes, this represents a maximum of 45.5 days.
The battery life for an application can be much greater than this value and will remain at a reading of 65535
until it drops below this. Life in percentage was added for this reason. Percentage will track starting at 100
percent and drop down as battery life decreases.
The controller can therefore use both registers, one to
represent usage in percentage to present to the user and then use the life in minutes to set a threshold on when
a low battery condition exists for changing the battery.
4.2.5 Register – uC Version
This is set to a value based upon the version of firmware programmed into the RXT-320 microcontroller. It is
stored as two byte value representing the major and minor revision numbers. So a 0113h (275 decimal)
represents a major version of 01 and minor version of 13. As software is updated this will be incremented
appropriately.
4.2.6 Register – Sleep Time
The Sleep Time represents the amount of time in seconds the RXT-320 will be in a low power sleep state. Its
main purpose is to provide a mechanism for place all RXT-320s in a system to sleep to conserve battery
power. If there are no batteries used within the network of RXT-320 transceivers this register is not utilized.