From: James Wages <james@kiramek.com>
To: "piclist@mit.edu" <piclist@mit.edu>
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Date: Fri, 23 Jul 2021 18:45:07 -0700
Subject: Re: [PIC] Automotive RS-485 & PIC18F25K80
Thread-Topic: [PIC] Automotive RS-485 & PIC18F25K80
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Alan,

I am sure there is NOT another pin on the ADM chip connected to what would =
be CAN-RX on the PIC.  I did indeed check pin-to-pin with a meter in Contin=
uity check mode.

The interface board I've been discussing only offers 4 wires in its wire ha=
rness:

1. +12V Power
2. GND
3. RS-485 "A"
4. RS-485 "B"

It comes with a custom made wire harness that splices the interface board's=
 4 wires onto 4 wires used by the factory head unit and then uses other wir=
es in that custom wire harness to pass all signals from an external third p=
arty CD/DVD player to the head unit.

In other words, it is not a situation where the interface "PCB" takes all t=
he wires from an external DVD player and then passes them through to the fa=
ctory head unit.  The interface board merely communicates with the factory =
head unit via RS-485 (2 wires only) to trick the head unit into believing t=
he externally connected DVD player is a factory unit.  Without that injecti=
on of code into the RS-485 data stream, the external DVD player will not be=
 recognized by the factory head unit.  I am trying to determine what that p=
rotocol is which allows third part devices to work with the factory head un=
it, as I am unable to find any similar protocol information available onlin=
e.  I am also trying to figure out why they used such a high end PIC18 rath=
er than just a PIC16.

Best,

James


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