Addressing

How to use addressing

  • Addresses are entered in hex format - i.e. 2 hex digits (0-A) are used to represent all possible values of a byte (0-255). For example AD would represent the vale 169 (=10*16+13).
  • Should you wish to monitor or display these addresses then it is advisable to use byte values which represent printable characters - i.e. the (decimal) range 33 to 126
  • A complete table showing decimal, hex and ASCII characters is given in appendix A of the Satel user guide.
  •  For small networks an easy solution is to use the hex values 30 to 39 which represent the printable characters 0-9. Thus a transmit address set as 3432 would prefix each data packet with “42”.
  •  A transmit address is prefixed to all outgoing data packets from that particular modem.
  •  A receive address acts as a filter. The first 2 bytes of every received data packet are checked against the address. If they don’t match the data packet is ignored. If they do the packet is received and sent to the RS232 (or RS485) interface.
  • By default the first 2 bytes (the receive address) are stripped from the data packet before it is sent to the RS232 (or RS485) interface. An option may be set so that the complete data packet is passed exactly as received.
  • The base station and all outstations only use the primary transmit and receive addresses
  • A repeater uses all 4 addresses. A data packet received using the primary receive address is repeated (re-transmitted) using the primary transmit address. A data packet received using the secondary receive address is repeated (re-transmitted) using the secondary transmit address.

    A simple example


Base Station                         Repeater                         Outstation

Transmit 3131 “11”>>>Receive 3131 “11”

                                Transmit 3231 “21”>>>  Receive 3231 “21”

 

                                             Receive 3230 “20”<<<    transmit 3230 “20

Receive 3130 “10”<<<   Transmit 3130 “10”

 

 

 

 

 

 

 

 

 

 

 

 


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