Last modified on 13 April 2014, at 00:43

FixmeBus

Revision as of 00:43, 13 April 2014 by Jhu (Talk | contribs) (Overview)

Overview

20140412 190054t.jpg

FixmeBus is a field bus based on the half duplex RS485 famous hardware protocol. It is a master / slave architecture, with every slave chained together.

The communication protocol is a standard UART, which has these following parameters:

  • 38,400 bauds
  • 8 data bits
  • 1 start and 1 stop bit
  • no parity
  • no flow control

Each end of the bus is terminated with a 1% 120R resistor.

Every data frame on the bus is like this (byte on the left = first byte):

  • 2 bytes of slave adress (ID_HIGH and ID_LOW) => 65536 slave adress
    • ID = 0 => Master
    • ID = 65535 => order to all slaves (no ack)
    • ID = 65000 to 65499 => order to a group of slave (no ack)
    • ID = 1000 to 64999 => order to an unique slave (ack)
  • 2 bytes for the function (FCT_HIGH and FCT_LOW)
  • 1 byte for the number of data bytes to transmit (N_BYTE)
  • n byte(s) of data (DATA) bytes (max. 200 bytes per frame)
  • 2 bytes for the CRC (CRC_HIGH and CRC_LOW)
b0 b1 b2 b3 b4 b5 ... bn+4 bn+5 bn+6
ID_HIGH ID_LOW FCT_HIGH FCT_LOW N_BYTE DATA[0] ... DATA[n-1] CRC_HIGH CRC_LOW

Technical Documents

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