1. internal counter C
The internal counter counts the internal signals (such as X, Y, M, S, T, etc.) when performing the scan operation. The connection and disconnection time of internal input signal should be longer than that of PLC.
(1) the 16 bit increase counter (C0 ~ C199) is 200 points, of which C0 ~ C99 is a general type, and 100 points of C100 to C199 are a power break retention type. This kind of counter is an added count. It sets a set value before application. When the number of input signals (rising edge) is added to the set value, the counter action is often closed and often closed. The setting value of the counter is 1~32767 (16 bit binary), and the setting value can be set indirectly through the specified data register in addition to the constant K setting.
The following example illustrates the working principle of a universal 16 bit increment counter. As shown in Figure 1, X10 is the reset signal and C0 is reset when X10 is ON. X11 is counting input. Whenever X11 is connected to a counter, the current value is increased by 1 (note that X10 is disconnected, and the counter will not reset). When the counter counts the current value to 10, the output contact action of the counter C0 is Y0 connected. After that, even if the input X11 is connected again, the current value of the counter remains unchanged. When the reset input X10 is connected, the RST reset command is executed, the counter is reset, the output contact is reset, and the Y0 is disconnected.
2. General auxiliary relay (M0 ~ M499)
The FX2N series has a total of 500 points with auxiliary relay. When the general auxiliary relay is running at PLC, if the power suddenly goes off, all the coils are OFF. When the power is switched on again, except for the external input signal, the remaining ON will remain OFF, and they will have no power failure protection function. General auxiliary relay is often used as auxiliary operation, temporary storage and shift in logic operation.
According to needs, the M0 to M499 can be changed to power failure to maintain auxiliary relay by program setting.
Power interruption relay (M500 ~ M3071)
The FX2N series has 2572 M500 to M3071 power cuts to maintain auxiliary relay. Unlike ordinary auxiliary relay, it has the function of power failure protection, that is, it can remember the instantaneous state of power interruption and reappear its state after re energizing. It can maintain its original state when the power supply is cut off, because the lithium battery in PLC keeps the contents of their image registers when the power is interrupted. Among them, M500 ~ M1023 can be set as universal auxiliary relay by software.