Unterminated S88 buss? Topic is solved

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Joined: 05.12.2017, 11:08
Location: West Hertfordshire, UK

Unterminated S88 buss?

Post by apemberton » 28.03.2019, 09:22

I had a problem with Rocrail which I could not understand. Rocrail was working but very slowly and the trace files were filling up with QueueOp reports very quickly. I couldn't understand what was going wrong.

As I had a change of heart about fitting a Digikeijs DR4088 with S88 to my DR5000, using, instead a DR5088 with Loconet. I thought I had an addressing problem (clash) so I changed the DR5088 but that didn't cure it.

I eventually connected the DR5000 to the Digikeijs control software through the USB to see what was going on. To my amazement, the feedback addresses 1 to 10 on the DR5000 were going beserk, flipping on and off. I wasn't intending to use a feedback address lower than 101 to avoid clashes. I deduced from these addresses that is where the S88 feedback addresses would be. But the device wasn't attached.

On inspection, I had left a 2 Metre RJ45 network cable attached to the DR5000 S88 port but not to anything else. Removing that cable stopped the problem instantly. I admit to being surprised that an unterminated cable of 2 Metres could have
such an effect and shows how sensitive the DR5000 S88 bus must be!

I had about 2 days head scratching and swearing fiddling with RR configurations. A simple removal of that cable could have saved a lot of angst! Foolish? Moi? I should have known better as I had the very same type of problem when working on computer networks in the 1970's with reflections back through the RS232 or Coaxial cable being amplified by the input transceivers (transistor in those days). :roll:

Lesson relearned!


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Re: Unterminated S88 buss?

Post by cds » 28.03.2019, 09:30

Hello Tony,

thank you for sharing your expierence with us.

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Re: Unterminated S88 buss?

Post by RainerK » 28.03.2019, 09:52

Hi together,

in a Bus system is an cable with an open end never a good idea and under experts an absolutely NO GO.

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