An automatic identification IO modules, IO consecutive numbers down by a physical connection. But the program even without the IO module may still running down. Because IO address is mapped to the cpu's memory, program memory operations generally.
2 software configuration and download it to the cpu to identify the IO module. Once the module occurs from such failure, cpu system plc communication modules fault alarm can be issued immediately, the hardware must meet the configuration settings, and IO address mapping can also be freely allocated memory space.
I / O expansion bus, there are many, output module plc various PLC manufacturers are different, or look at the refresh rate. Slow, then you can use SPI and the like, and then a little faster, then you can do a physical interface with FPGA, there is one of the fastest Industrial Ethernet.
Simple application can even use the serial port to do. I / O port expansion is the I / O address to the CPU memory map, but plc logic controller this map is a combination of software and hardware self-identification are defined manually or through assignment and allocation. May be in the exhaust line is whether there should be a line behind the front of the module has a successor in charge of the report module, if the module behind the successor state that level on this line, and when no module is not the same, so that they can be judged No follow-up module, CPU module communicates with other modules using the relay mode, the transmission down a level, that is, only the CPU module and from his recent communication module, output module plc and other modules if you want Communication would have to transit through plc controller manufacturer other modules, so that modules are installed in accordance with the order of the address of the module can be determined, on power CPU perform a self-test program, each module to report their labeling information so that you can know the total CPU module the number of mounted modules, each module location and type of each module.
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