Transmission of S88 data over network cable
- The S88 bus is established as inexpensive feedback bus for model layouts.
It follows a simple principle: the S88 bus is just a serial shift register
with parallel load entries.
In order to minimize disturbance during the transmission, a switch over to cheap network cables for wiring is recommended.
The advantages of CAT-5 cabling and RJ-45 plug connectors are also recognized by other designers. Unfortunately there are different pin assignments. Standardization took place mid of 2007. Future developments should use this standard s88-N. There are already some products and announcements, like from Tams Elektronik, Blücher Elektronik, Sven Brandt (digital-bahn.de), Paco (NanoX-S88), Huib Maaskant (modules and adapter), RoSoft by Wim Ros, and rocrail (ORF-1). OpenDCC supports S88-N from HW revision 1.4.
(*) RAILDATA should be routed through even when not used.)
(Click to logo to get a better image)
The use of the logo, of the name s88-N and the cable pinning is free of charge.
However, to ensure the compatibility between different devices, following rules must be observed:
- pinout according to the above table
- compliance with the timing requirements and publication of the implemented timing.
- clear indication whether 5V - 12V operation is supported. li>
- clear indication whether RAILDATA (with or without feedback) is supported. li>
The logo and name is copyrighted by Kersten Tams and me. Any usage which extends the signing of modules and components
of compatible to s88-N requries a written approval of the copyright owners.
Modules which are not conform to the above specification and condition are not not allowed to use the logo.
Every user of the logo and the name s88-N must announce this to the copyright owners. (with mail).
Every user has to reference to the source of the logo (could be a link to either http://www.opendcc.de, http://www.digital-bahn.de or http://www.tams-online.de).
|schematic adapter S88-N||pcb layout adapter S88-N|
The following components can be used (order number according to reichelt.de):
- MEBP 8-8 (double socket to extend a CAT-5 cable)
- MEBP 8-8S (socket for pcb)
- BL 1X20W8 2,54 (socket for S88 header; this one comes with 20 pins and can be divided in pieces with 6 pins each)
- CAT5 cables: also available at Reichelt, seek for 'RJ45'
Overview and comparison of past assignments s88 to RJ45
- The assignments of railway lauf.de and iek.de are electrically unfavorable, because the sensitive lines are not paired with static lines. Both assignment were obviously driven by the wish of having a simple pcb layout. To make things worse, the assignment of IEK does not strengthen the GND.
- A possible higher supply voltage of 12V and an appropriate shift of the threshold for the signals offers more margin, so that disturbances cannot affect the signal lines. Therefore also the 12V supply was allowed as an alternative to the 5V supply. The user must pay attention that only if all attached modules are tolerant to the higher supply than 12V may be turned on by the command station or by a s88 booster. Therefore this 12V supply may cause damage in the field, so in my opinion only 5V should be used.
- In the assignment of digital bahn.de the RESET line was omitted, which may cause compatibility problems. The RESET line is contained in s88-N.
- The optimal GND assignment of opendcc was weakened in favor of RAILDATA (i.e. the track signal).
- To avoid uncontrolled GND-loops or loss of secure isolation, the cable shield should be left open.
|Overview of past assignments s88 to RJ45|
|Vendor / Standard|
Following my comments on these pinnings: