GE PACSystems RXi User Manual

Chapter 5. CPU Operation88 PACSystems* RXi Distributed IO Controller User Manual GFK-2816FTo recover from Stop-Halt mode and return to normal operation, all non-volatile memory mustbe cleared. This can be done by disconnecting the Energy Pack and power cycling the unit. Ifpower cycled with the Energy Pack connected, the CPU returns to Stop-Halt mode andretains all non-volatile memory, including fault tables.5.8.4 Timed ContactsThe PACSystems has four timed contacts that can be used to provide regular pulses ofpower flow to other program functions. Timed contacts cycle on and off, in square-wave form,every 0.01 second, 0.1 second, 1.0 second, and 1 minute. Timed contacts can be read by anexternal communications device to monitor the state of the CPU and the communicationslink. Timed contacts are also often used to blink pilot lights and LEDs.The timed contacts are referenced as T_10MS (0.01 second), T_100MS (0.1 second),T_SEC (1.0 second), and T_MIN (1 minute). These contacts represent specific locations in%S memory:#T_10MS 0.01 second timed contact %S0003#T_100MS 0.1 second timed contact %S0004#T_SEC 1.0 second timed contact %S0005#T_MIN 1.0 minute timed contact %S0006These contacts provide a pulse having an equal on and off time duration. The following timingdiagram illustrates the on/off time duration of these contacts.XX/2SECT XXXXXX/2SECSECCautionDo not use timed contacts for applications requiringaccurate measurement of elapsed time. Timers, time-basedsubroutines, and PID blocks are preferred for these types ofapplications.The CPU updates the timed contact references based on afree-running timer that has no relationship to the start of theCPU sweep. If the sweep time remains in phase with thetimed contact clock, the contact will always appear to be inthe same state. For example, if the CPU is in constant sweepmode with a sweep time setting of 100ms, the T_10MS andT_100MS bits will never toggle.For additional information using the timed contacts instructions, refer to the Proficy MachineEdition online help.