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# CONV-TTL-RS485 RTM in DB9
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An RTM for the CONV-TTL-RS485 board has already been designed and
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tested. It is a 6 channel RTM with each channel capable of receiving one
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input in RS485 and repeating it on 3 outputs.
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This RTM uses LEMO 0S connectors with 2 pins.
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A new RTM design for the CONV-TTL-RS485 is being proposed to fullfill a
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number of user requirements:
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- **User requirements** (CERN specific):
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- Most of the legacy boards to be replaced by the new generation
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repeaters, use a D-Sub 9 connector for the RS485/RS422
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interface. The proposed LEMO 0S RTM is therfore not a drop-in
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replacement.
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- The use of the RS485 protocole is mainly required in fanout
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topologies, where one signal must be propagated to multiple
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locations. The 6 channels on the LEMO 0S RTM, although offer 3
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outputs each, still need to be manually daisy chained in order
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to offer a maximum number of output signals.
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<!-- end list -->
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- **Proposed solution**
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- Design a new RTM with D-Sub 9 interface for I/O.
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- The RTM will repeat 2 channels of the 6 available from the
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conv-ttl-rs485 board.
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- Each of the two channels will repeat the input signal on 5
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output ports (Limited by the physical size of the RTM Piggyback
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panel).
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- The RTM must be designed in the *piggyback* format, in order to
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be mounted on the same [RTM
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motherboard](https://edms.cern.ch/project/EDA-02452)
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used for
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[CONV-TTL-RS485](https://www.ohwr.org/project/conv-ttl-blo/wiki)
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and
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[CONV-TTL-BLO](https://www.ohwr.org/project/conv-ttl-blo-hw/wiki)
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RTMs.
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-----
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Denia Bouhired, 21 Septembre 2017
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### Files
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* [db9rtm-mockup-small.png](/uploads/4e78ed0f4b6eb5512980a1cd143d7622/db9rtm-mockup-small.png)
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* [db9rtm-mockup.PNG](/uploads/16f77ac7d87a9cffa6a78b20e7fb745a/db9rtm-mockup.PNG) |
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