On 16.08.2021 23:10:29, Vincent MAILHOL wrote:
[...]

After the discussion I had with Stefan, I assumed mcp251xxfd also
used relative TDCO.  However, in the mcp15xxfd family manual,
Equation 3-10: "Secondary Sample Point" on page 18 states that:

| SSP = TDCV + TDCO

As I commented above, this is the formula of the absolute
TDCO. Furthermore, in the example you shared, TDCO is
16 (absolute), not 0 (relative).

ACK

*BUT*, if this is the absolute TDCO, I just do not get how it can
be negative (I already elaborated on this in the past: if you
subtract from TDCV, you are measuring the previous bit...)

Another thing which is misleading to me is that the mcp15xxfd
family manual lists the min and max values for most of the
bittiming parameters but not for TDCO.

Finally, I did a bit of research and found that:
http://ww1.microchip.com/downloads/en/DeviceDoc/Section_56_Controller_Area_Network_with_Flexible_Data_rate_DS60001549A.pdf

Interesting. This data sheet is older than the one of the mcp2518fd.

This is *not* the mcp25xxfd datasheet but it is still from
Microship and as you will see, it is mostly similar to the
mcp25xxfd except for, you guessed it, the TDCO.

It reads:
| TDCMOD<1:0>: Transmitter Delay Compensation Mode bits
| Secondary Sample Point (SSP).
| 10 = Auto; measure delay and add CFDxDBTCFG.TSEG1; add TDCO
| 11 = Auto; measure delay and add CFDxDBTCFG.TSEG1; add TDCO
| 01 = Manual; Do not measure, use TDCV plus TDCO from the register
| 00 = Disable

| TDCO<6:0>: Transmitter Delay Compensation Offset bits
| Secondary Sample Point (SSP). Two's complement; offset can be
positive, zero, or negative.
| 1111111 = -64 x SYSCLK
| .
| .
| .
| 0111111 = 63 x SYSCLK
| .
| .
| .
| 0000000 = 0 x SYSCLK

Here, you can clearly see that the TDCO has the exact same range
as the one of the mcp25xxfd but the description of TDCMOD
changes, telling us that:

| SSP = TDCV (measured delay) + CFDxDBTCFG.TSEG1 (sample point) + TDCO

Which means this is a relative TDCO.

I just do not get how two documents from Microchip can have the
TDCO relative range of -64..63 but use a different formula. I am
sorry but at that point, I just do not understand what is going
on with your controller...

Me neither. I'll ask my microchip contact.

regards,
Marc

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