05704-A-0145 |HONEYWELL| Basic Control Principles

Description

05704-A-0145 |HONEYWELL| Basic Control Principles

05704-A-0145 can be divided into input part, logic part, and output part
Input section: It collects and saves data and information on the actual operation of the controlled object. For example, it collects various switch information from the controlled object or operation commands from the control panel.
Output section: Provide which devices need real-time operation and processing among the many devices being controlled.
1. 05704-A-0145 working process
PLC adopts a cyclic scanning working mode, which is very different from other microcomputer working modes. The microcomputer control adopts a waiting command working mode, such as the common keyboard scanning mode or I/O scanning mode. If there is a key press or I/O action, it will enter the corresponding subroutine, and if there is no input, it will continue to scan.
1.1 Scanning cycle of PLC
The working process of a programmable controller includes two parts: a fixed process for self diagnosis and communication response, and a user program execution process, as shown in Figure 5-1. Before each execution of the user program, the PLC first executes internal fixed programs such as fault self diagnosis, reset, monitoring, and timing. If the self diagnosis is normal, continue scanning downwards, and then the 05704-A-0145 checks for communication requests with the programmer, computer, etc. If there are communication requests with computers, etc., corresponding processing should be carried out. When the PLC is in the STOP state, only the first two processes are cycled. When the PLC is in the RUN state, it cycles through five working stages: internal processing, communication operations, input scanning, executing user programs, and output refreshing. The time required to complete each of the five stages is called a scanning cycle.