S88n - Specification

Current situation 20.03.2023

This standard has been documented by the RailCommunity under RCD-688 (RCD-688.pdf)

Transmission from S88 via network cable

Current situation:

The S88 bus is established as an inexpensive feedback bus for model layouts.
Technically speaking it is not even a data bus, but one big shift register. The feedback decoder translates its contacts into bits and bytes. When the status of the contacts is read, all the bits are pushed one by one to the central unit. There is no error correction or any other technique to suppress errors

Its simple nature make the S88 bus vulnerable for disturbance during the transmission. A switch over to cheap network cables will greatly reduce the errors while reading the feedback modules.

The advantages of CAT-5 cabling and RJ-45 plug connectors are also recognised by other designers. Unfortunately everybody used different pin assignments. Mid 2007 a standard was developed to make the new generation of S88 decoders compatible: s88-N. Future developments should use this standard s88-N . There are already several manufacturers who have adopted the new standard. Here are links to those manufacturers.

Pin allocation

	s88-N: Standardization of s88 on network cable (CAT-5, RJ45)
Pin S88	Name	Description	Pin RJ45	color (**)
1	DATA	data to read	2	gn
2	GND	Return (Ground) for signals and power supply	3	wt/or
2	GND		5	wt/bl
3	CLOCK	clock signal for shifting data	4	bl
4	PS (LOAD)	load request for slave devices	6	or
5	RESET	clear the slave devices	7	wt/br
6	+5V/+12V	power supply to feedback modules	1	wt/gn
-	RAILDATA *)	track signal (e.g. DCC or MM) *)	8	br
-	SHIELD	cable shielding, not connected	-	-

(*) RAILDATA should be routed through even when not used.)
(**) Color coding according to Ethernet cable standard EIA/TIA 568A
(Click to logo to get a better image)

Guidelines

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:

Pin-out according to the above table
compliance with the timing requirements and publication of the implemented timing.
Clear indication whether 5V - 12V operation is supported.
Clear indication whether RAILDATA (with or without feedback) is supported.

The logo and name is copyrighted by Kersten Tams and Wolfgang Kufer. Any usage which extends the signing of modules and components compatible to s88-N requires 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 https://www.opendcc.de, https://www.digital-bahn.de or https://www.tams-online.de).