TPPL – Twisted Pair Physical Layer
In January 2019, the 3rd revision of ISO 11783 – Part 2: Physical Layer has been published. As you may know this part of the ISO standard details the requirements for the physical layer of ISOBUS systems and includes the tests to be performed to verify that a device can be considered electrically compliant to the standard.
This new release comes after a long period of hard work, carried out in AEF PT3 and ISO, that was initially kicked off after the ISO TC23 SC19 plenary meeting held in Tokyo in the month of April 2013. The first couple of years were used to identify the technical specifications in order to find a trade-off between the demands coming from different markets and manufacturers. After a common interpretation was agreed and blessed by the AEF Steering Committee, the technical activity actually began.
The AEF PT3 subgroup named “Simplified Physical Layer” (this was the original name for the new physical layer) started the prototyping phase by performing tests to check how the new bus system behaved, specially by considering the strong requirement for a complete backward compatibility with “legacy” ISOBUS systems and machines (with “legacy” are intended systems based on the Twisted Quad Physical Layer, as detailed in the previous version of the standard).
When the technical requirements were mature and verified, ISO put all of them in the new revision of ISO 11783-2 and, in the meanwhile, the concept changed name a couple of times to COPL (Cost Optimized Physical Layer) first and eventually to TPPL which stands for Twisted Pair Physical Layer and that was chosen in order to clearly distinct it from the TQPL, Twisted Quad physical layer, at the base of all ISOBUS machines today on the market.
To be completely honest, the TPPL concept is nothing new: the technology is very mature and widely used in all passenger cars and the physical layer is based on SAE J1939-15 (Unshielded Twisted Pair specification). However, AEF spent a lot of time to verify that it was working with no issues on agricultural machines with the requirement of “plug and play” or “hot plug” connections foreseen by the ISOBUS.