C h a p t e r 5 D e v i c e5 - 5Device typePLC actionNon-latchedareaLatchedarea Output relay(All latched areas are cleared.)Default value 0 0 05.1.4 Latched Areas in the Device RangeDevice Function Latched areaX Input relay All devices are non-latched.Y Output relay All devices are non-latched.M* Auxiliary relay The default range is M0~M8191.SM Special auxiliary relay Some devices are latched, and cannot be changed.Please refer to the list of special auxiliary relays for more information.S Stepping relay All devices are non-latched.T* Timer The default range is T0~T2047.C* Counter The default range is C0~C2047.HC* 32-bit counter The default range is HC0~HC63.D* Data registerAH500-EN/RS2: The default range is D0~D16383.AH501-EN/RS2: The default range is D0~D24575.The default range is D0~D32767.At most 32768 devices can be latched areas.SR Special data register Some are latched, and can not be changed.Please refer to the list of special data registers for more information.L Link register All devices are non-latched.E Index register All devices are non-latched.*: * indicates that users can set the range of latched areas, and that the device can be set to Non-latched Area.The range of latched areas can not exceed the device range. Above all, only 32768 data registers at mostcan be non-latched areas. For example, users can set D50~D32817 or D32768~D65535 to Latched Areasalthough the default range of latched areas is D0~D32767.5.2 Functions of DevicesProcedure for processing the program in the PLC:Input ter minal XDevice memoryProcessin g th e prog ramD e v i c em e m o r yRegener ating the output s ignaland sending it to the output ter minalRegener ating the input signalDevice memory Regenerating the input signal1. Before the program is executed, the state of theexternal input signal is read into the memory of theinput signal.2. When program is executed, the state in the memory ofthe input signal does not change even if the inputsignal changes from ON to OFF or from OFF to ON.Not until the next scan begins will the input signal berefreshed. Processing the programAfter the input signal is refreshed, the instructions in theprogram are executed in order from the start address of theprogram, and the results are stored in the devicememories. Regenerating the state of the outputAfter the instruction END is executed, the state in thedevice memory is sent to the specified output terminal.
