Syvecs Forums

Does the X10 need a 120R resistor across CAN 1 when connecting to Life F88R CAN 2?

I've measured the impedance across the pins (26,27) and it's open circuit.

Yes - as per X10 manual

That document is wrong, there is no need nor requirement to add a resistor and if you do it will cause no end of headaches, as I found out on one customers car.
that special CAN link is just wired up and that is it (no termination resistor).

"CAN2 from ECU is wired directly to CAN1 of the X10
Also both the F88 and X10 has CAN termination already built in so please ensure you have not fitted any external CAN termination resistors in your wiring, if so please remove them."

The (couple of) wiring schedules I have from Syvecs for loom adapters that need the X10 state the resistor is required. As does their documentation. Never had any issues when wired up like this.

If no resistance is being measured by the OP at the X10 CAN pins, then it will need a resistor. The ECU has one, yes, but I still don't believe the X10 has one.

I used a customer supplied Syvecs X10 to a full LR F88 and it had drop out issues and Life Racing X10 document states no termination resistor required and their senior applications engineer told me to remove it (as I followed the Syvecs doc, forwarded that originally by my regional distributor) so I found out the hard way that it was/is wrong.


p.s. The X10 would drop out. Upon removal of termination resistor as per LR directive all problems stopped.

http://www.liferacing.com/wp-content/do ... %20X10.pdf

Thanks, two different opinions, hence my original question.

I'll try without the termination resistor first.

Once you have wired it in, measure the resistance (with power off). If it's 60 ohms: fantastic. If it's 120 ohms, you need a termination for it to behave correctly.

And please report back!

I'll not presume to bore everyone with the full spec, from Bosch, as to the correct termination of a CAN bus, nor the permissible stub length etc.... what I will state is that a CAN bus needs to be terminated at both ends. Given that the S* ECUs are terminated, they must be at one end, they cannot be anywhere else. The X10 should not have internal termination, hence it may be at the end of a bus, or it may be in the middle. The determination of whether to fit a terminator to an X10 is entirely predicated on its location on the bus - if it is at the end then it must be terminated, if it is in the middle then it must not be terminated. Moreover, the bus must be a "daisy chain", going from one device, to the next, to the next, etc, all the way to the far end. It cannot be a star topology. It cannot be a ring. It is a daisy-chain. If you do not follow these simple rules then the bus will break - the longer it is the easier it is to break.

A CAN bus' wires are an electrical tranmission line with a characteristic impedance of 120 ohms. In order to prevent signal reflections at the ends of the bus, the impedance looking "into" the space "beyond the end" must be 120 ohms. Signals passing a device half way along are doing just that - passing. Now imagine a device 2/3rds of the way along starts a transmission - it could reflect off the near and and then the reflection could interfere with the rest of the transmission. Broken bus results. If, however, the impedance at either end of the bus matches the characteristic impedance of the transmission line then the signal will be completely absorbed and nothing gets reflected - the end device can still "see" the signal, but after that it disappears out of harm's way.

If a bus is is experiencing issues, despite there being two terminators on it, it almost invariably means that the wiring is at fault - either because the rules of how to organise a CAN bus have not been followed, or because the wires themselves have the wrong characteristic impedance. The only time it is "OK" to break these rules is if the bus is shorter than the permissible stub length, then you can sometimes get away with just one terminator - in extremely rare cases you can get away with none, but it is a really bad idea. Even if the bus is really short, properly terminating it at both ends is still a good practice - it will certainly not make it any worse.

Hope this helps,

Pat.

X10: is on its own CAN link as posted above F88 > X10 (nothing else in the chain) and from LR directly said to not run a termination resistor (email to me).
They also told me the document from Syvecs was wrong (this is the one I originally followed).
Wiring is perfect 20AWG, twisted, screened, and grounded one end. The only issue as identified was incorrect advice stating that a termination resistor was required to run it as a slave to the F88. I only know and I found out after having many issues with the connection, it turned out to be the fitment of the 120ohm at the X10 end, and once removed all issues went away .

Other items on the other F88 CAN1 link daisy chained with termination at end of bus F88 > D5 > *third party device* > GPS all work flawlessly. I know cause I wired it myself It was only the F88 > X10 'slave' link that gave trouble, once following the correct advice the trouble went away.


FYI There is other issues with the X10 that means it will drop out signal upon first few degrees of crank rotation is the battery voltage during that stage is below the threshold they set for operation (mind you for a fraction of a second only), had to log at ~250hz to catch that 'issue' in this customers case its cause running E85 strategy and using the ethanol content sensor through the X10 meant it would not reference the correct maps during cranking (I.E. pain in the arse, cause Ethanol was false 0% due to low voltage spike, even though cranking voltage was healthy/normal, we even tried a brand new battery too.) Only solution to that was to change out that input over to a F88 input channel rather than through the X10..... another trap for young players.

Learned allot about the X10

It's all connected up. Unfortunately due to the Formula Ford security on the ecu I can't verify that it's working until I drag it to Northampton Motorsport for the dyno session where they will have access to the Life Hq licence server and will be able to verify it's status.

This is what it's being used for, paddles, launch and ti-vct