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The ELPRO 105 modules use a very reliable transmission protocol designed for secure communications, even with external interference. Because 105 modules have transceivers, modules are able to communicate with each other to control the flow of information.
Transmissions occur when an input signal changes. That is, when a digital (switch contact) input turns off or on, or when the value of an analogue input changes by a pre-configured amount. The 105 provides real-time communications, which polling systems cannot achieve.
There are also regular update transmissions to check the value of the input signals and to check the integrity of the communication path. The status of the communications path is available as an alarm output.
The input signals are transmitted in a "data frame" which includes the address of the transmitting module, the address of the destination module, and a CRC error check. The error check is used to ensure that there is no corruption of the data frame during transmission.
Each module will wait until the radio channel is "free" before transmitting a message. When the destination module receives the message, it will check the validity of the message and transmit a return acknowledgment - a "handshake". If the original module does not receive this acknowledgment, then it will resend the message another four times. Using this simple but secure communications protocol, the 105 provides reliable operation even in noisy environments.
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