Plc is in the RUN mode and repeats the five phases of the task shown in Figure 1-2. In the STOP mode, only the tasks of the above two phases are performed.
In the internal processing stage, the PLC completes internal work such as hardware self-test and resetting the monitoring and positioning time. During the communication service phase, the PLC processes communications with computers, programmers, and other smart devices. The working mode of a cyclic execution task of a PLC is called a scanning mode of operation.
In the PLC's memory, an area is set to store the state of the input and output signals, which are called input image registers and output image registers (see Figure 1-3). Other programming elements in the PLC ladder diagram also have corresponding image memory areas, which are collectively referred to as component image registers.
In the input processing phase, the PLC reads the on/off states of all external input circuits in a centralized manner and stores them in the input image registers in the form of binary numbers.
The user program of the PLC consists of several instructions, which are sequentially arranged in memory. When there is no jump instruction, the CPU starts the first instruction and executes the user program one by one in sequence, until the user program ends. When the instruction is executed, the 0, 1 state of the programming component is read from the component image register, and the corresponding logic operation is executed according to the instruction requirement, and the final operation result is written into the component image register corresponding to the coil or the output class instruction. .
During the output processing phase, the CPU centrally transfers the 0, 1 state of the output image register to the output module. The input and output modes of PLC are called batch input and batch output.
With the rise of 4G network construction in the world, multi-network operation has become the main melody of the network development of operators. Qingdao Unicom's current network status is 2/3/4g coexistence. In the optimization and adjustment, the ideal situation is that 2/3/4G network can have its own independent antenna, so that RF adjustment is convenient and flexible. However, due to the constraints of antenna installation site resources, space shortage, construction cost and other factors, common antenna strategy can only be adopted in network construction in many cases, which not only saves resources, but also brings difficulties to RF adjustment and multi-network coordination optimization. In view of this situation, the Network Optimization Center of Qingdao Unicom combined with the actual situation of the network, made a statistical study of various common antennas, and made an analysis and adjustment plan according to the network demand. There are a large number of 2/3/4G common antenna sites in the current construction. According to statistics, the proportion of common antenna in the current network is over 60%, which is higher than the national average level. Three, the current total antenna situation classification 1. 2/4 g share a common antenna by 2/4 g RRU type of antenna and antenna panel. 2. 3/4G common antenna is divided into: the beautification antenna cannot be adjusted independently, the circuit board antenna cannot be adjusted independently, and the common antenna can be electrically adjusted independently. 3. 2/3/4/G common antenna is divided into: 2/3/4/G common antenna cannot be independently adjusted, and 2/3/4/G common antenna can be independently electrically adjusted. Four, common antenna formation reasons and advantages and disadvantages
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