Communication interface modules are used to build decentralized I/O stations in decentralized
systems. They contain the fieldbus interface and a set of onboard I/O channels. Additional I/O
modules can be attached to build larger decentralized I/O stations. A communication interface
module is mounted on a terminal unit.
Function modules extend the PLC system to perform special task control. These modules often
provide independent components such as a CPU, system programs, memory and interfaces
connected with the PLC system bus.
Function modules are connected with the PLC via the I/O bus to exchange data and independ-
ently work under cooperative management of the PLC.
In the PLC, the memory is mainly used for saving system programs, user programs and work
data. There are two types of memory:
● Volatile memory:
All saved data will be lost after power failure of the memory but the memory can provide
a high access rate and unlimited programming cycles. Common volatile memories mainly
include SRAM and DRAM (including common memories such as SDRAM).
● Nonvolatile memory:
All saved data will not be lost after power failure of the memory, but the memory is subject
to a low read-write rate and limited rewrite cycles. Common nonvolatile memories mainly
include NORflash, NANDflash, EEPROM, memory card, etc.
AC500 PLCs store all user programs in the nonvolatile memory to protect them from power
failure. The programs are exported to the volatile memory during operation of the PLC to ensure
high-speed and efficient operation. If user program debugging is finished, the programs can be
fixed in the nonvolatile memory when they need no change. The work data is subject to frequent
change and access during the PLC operation. It is saved in the volatile memory to meet the
requirements for random access.
The work data memory of the PLC has the memory area for input and output relay, auxiliary
relay, timer, counter and other logic devices. The state of these devices depends on initial
setting and operation of the user programs. Some data maintains its existing state by using
built-in supercapacitors or backup batteries in the event of a power failure. The memory area for
data saving in the event of a power failure is called the data retention area.
The PLC is equipped with a switching power supply for the internal supply. In comparison with
an ordinary power supply, the switching power supply has a higher stability and a higher noise
immunity.
Some modules include a stabilized power supply for the supply of external sensors.
Communication
interface
modules
Function
modules
Memory
Power supply
System overview
AC500/S500: Short description hardware
2023/03/03
3ADR011074, 1, en_US
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