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Date: Fri, 23 Jul 2021 04:40:18 -0700
Subject: Re: [PIC] Automotive RS-485 & PIC18F25K80
Thread-Topic: [PIC] Automotive RS-485 & PIC18F25K80
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On Fri, 23 Jul 2021 08:56:45 +0900
James Wages <james@kiramek.com> wrote:

....
> On the "interface" PCB I have been discussing (which connects to
> Toyota "Display Audio"), I see the following: PIC pin 23 connects to
> DI on the ADM3078E chip. PIC pin 25 connects to RE* & DE on the
> ADM3078E, which are tied together. *RE "NOT"
>=20
> As per the PIC Datasheet...
> Pin 25 =3D RB4/AN9/C2INA/ECCP1/P1A/CTPLS/KBI0
> Pin 23 =3D RB2/CANTX/C1OUT/P1C/CTED1/INT2
....
> Madscientistatlarge, you suggested it could be a CAN protocol.  But
> if that were true, I would expect both CANTX and CANRX to be used.
> But while Pin-23 supports CANTX, Pin-25 does not support CANRX.


Step back a minute and look at the ADM chip pin functions. DE and /RE
are the data direction pins for the ADM, so when they are low it is
receiving and when high it is transmitting (or the other way around -
check datasheet). This means that DI is a data pin. Now I haven't
checked the data sheet, but this could be a bidirectional data pin
(direction dependant on DE and /RE) or seeing it is DI I would take
that to be Data In, i.e. that may be the transmit data pin. So it could
still be a CANTx, but what would initiate a transmission?

As the ADM chip uses logic levels you can leave all the analogue
functions of bot PIC pins out of the equation.

Are you sure there is not another pin on the ADM chip connected to what
would be the CANRx pin on the PIC? Checked pin to pin with an ohmmeter?

Does this board go between the DVD unit and the rest of the system,
i.e. a pass through for the digital audio to the head unit? If so that
is more likely to make the communication stream CAN I would have
thought, but could still be some proprietary protocol.

If this board doesn't act as a passthrough for the audio how is the
audio fed into the rest of the unit?




--=20
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