MX-RTC is an optional battery backed real time clock module that you add between the 28pin SRAM and the 28pin socket on any T100MD+ or T100MX+ PLC. It keeps the real time clock running even when all power to the PLC has been shut down.
If you turn on DIP Switch #1 to the PLC, then MX-RTC will preserve the values of all the internal variables when power is removed. These includes A to Z, A$ o Z$, DM[1] to DM[4000], as well as timers and counters present value.
There are also data and logic states that are NOT PRESERVED,such as the values of INPUT[], OUTPUT[], PWM output, DAC outputs and Stepper motor ouputs. The PLC will reset all the outputs regardless of the presencee of MX-RTC. This is to prevent a situation where after a power failure, some outputs that should NOT be turned ON unless with some user intervention to ensure that it is safe to do so, became active due to its ON state before power failure.
As such a scenario may be hazardous, it was decided that the output logic states will not be preserved after a power on reset. However, all internal relay logic status are preserved. So if your program requires that an output must return to its pre-power down states, then you can turn on an internal relay first and the contact of the internal relay is then used to drive the output. This give a degree of control to the user to determine which output is allowed to be turned ON based on its pre-power down logic state. Similarly, all PWM output and DAC outputs will not be set to their pre-power down values, so the programmer must take this fact into consideration.
