Resistor value applied between CAN H & L

[homerisback]

Hi guys,
While struggling to order SN65HVD234DR due lack of stock @ Mouser, I tried to find any equivalent chip but no luck, I'll wait for it.
By the way, I looked at its datasheet and saw that they talk about a 60 ohm resistor between CAN H & L lines where we use a 68 kohm one.
What led to this value and why is there a multiplying factor of 1000 in BlueSaab's design ?
Every module I built with 68 kohm obviously works fine, I only wanted to know if there's a reason I'm missing...
Thanks

[Seth]

This is because the canbus lines are *supposed* to have 120ohms between them. But I think Saab did something unique and I wanted BlueSaab to match that as much as possible.

with the additional esd protection diode, it changed the resistance so I seem to remember measuring something close to 120ohms across them (but different).

I also seem to remember comparing a stock cd changer resistance on the can lines and the BlueSaab module now reads similar to that.

On Mon, Mar 15, 2021 at 08:36 homerisback [via BlueSaab Forum] <[hidden email]> wrote:

Hi guys,
While struggling to order SN65HVD234DR due lack of stock @ Mouser, I tried to find any equivalent chip but no luck, I'll wait for it.
By the way, I looked at its datasheet and saw that they talk about a 60 ohm resistor between CAN H & L lines where we use a 68 kohm one.
What led to this value and why is there a multiplying factor of 1000 in BlueSaab's design ?
Every module I built with 68 kohm obviously works fine, I only wanted to know if there's a reason I'm missing...
Thanks

01' 9.3 SE Conv - AS3 - Nexus 5 Android M 6.0.1 - BlueSaab v4.2 + Amp - Latest CDC repo.

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[homerisback]

Thanks for your quick reply Seth, I didn't think Saab made it its own way... as they always did

[HenrikD]

If I have understood the CAN bus correctly, the 120 Ohm termination is only on the "outer most" unit. So when multiple units are connected to the same bus, it is only 1 unit that terminates with the 120Ohm between the CAN H and CAN L. When talking about 60Ohm, this is due to a split termination circuit, where the approach is 2 x 60Ohm in series between CAN H and CAN L (120 Ohm). The center between the two are connected with a capacitor to ground to reduce noise.