I've been reading about MIL-STD-1553 buses, which very briefly are

  • multidrop
  • Manchester-encoded
  • 1 Mbit/sec
  • 32-station: a single "bus controller" master and multiple "bus terminals" slaves which speak only when spoken to

Given how similar the two buses are electrically ...

I was wondering if it's possible to replace the electrical layer with RS-485?

This is an engineering-curiosity question for an industrial application: don't worry, it's not in a fighter jet!

Wikipedia shows a 1553 slave responding to the master's transmit instruction like this: enter image description here (source)

Is there any reason we couldn't do this pretty much exactly with an RS-485 transceiver? [Edit for clarification] By which I mean replace all the 1533 transceivers, transformers and cables with RS-485 transceivers, cables, terminators, cutting at the red line of the diagram below.

A typical 1553 transceiver looks like this: enter image description here (from DDC-8553 datasheet)

It's not clear to me why the transceiver has differential connections to the the decoder and encoder (ie to the right), but I'm guessing it's for signal quality.

As far as I can tell, something like this with a classical 75176-format RS-485 transceiver should work identically as far as the interfaced device is concerned (assuming suitable RS-485 wiring, lengths, termination etc):

enter image description here

Any reason that wouldn't work?

  • 2
    \$\begingroup\$ I see an isolation transformer and that means good control of DC voltages on the line and I don't think RS485 pays excessive attention to this. \$\endgroup\$ – Andy aka Jan 16 '20 at 14:56
  • \$\begingroup\$ Thanks @Andyaka ... I've edited my question to be a little clearer: I'm not asking about signal quality or isolation etc on the bus, I'm asking if the interface into the transceiver (right-hand-side) can tell if we replace the 1533 transceivers, transformers and cables with RS-485 transeivers (with extra gates for polarity and ignoring the differential /TXDATAIN), and use RS-485 cables terminators etc. \$\endgroup\$ – jonathanjo Jan 16 '20 at 15:08
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    \$\begingroup\$ @jonathanjo I expect it will work in a lot of applications but check out the NAND gate that disables transmission should both TXDATA and nTXDATA both be high. \$\endgroup\$ – Andy aka Jan 16 '20 at 15:17
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    \$\begingroup\$ 1553 is a three state bus (+, -, zero), the 1533 decoder will expect to see all three at the proper times. RS-485 will not simulate the zero state very well. I am guessing that it will not work. \$\endgroup\$ – Mattman944 Jan 16 '20 at 17:09
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    \$\begingroup\$ OK, if you are designing you own encoder/decoder, you should be able to compensate (for the missing zero state). Realize that designing an encoder/decoder is a big undertaking. \$\endgroup\$ – Mattman944 Jan 16 '20 at 18:37

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