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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