From: James Wages <james@kiramek.com>
To: "piclist@mit.edu" <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Sun, 25 Jul 2021 22:27:59 -0700
Subject: Re: [PIC] Automotive RS-485 & PIC18F25K80
Thread-Topic: [PIC] Automotive RS-485 & PIC18F25K80
Thread-Index: AdeB4J7EImAC2zbVRBi6D4J2OCOpYw==
Message-ID: <2F35BBEB-5F76-4E46-9430-21C0F901835B@kiramek.com>
Reply-To: Microcontroller discussion list - Public. <piclist@mit.edu>
Accept-Language: en-US
X-MS-Exchange-Organization-SenderIdResult: TempError
X-MS-Exchange-Organization-PRD: mit.edu
X-MS-TNEF-Correlator:
received-spf: Pass (protection.outlook.com: domain of kiramek.com designates
	72.52.183.109 as permitted sender) receiver=protection.outlook.com;
	client-ip=72.52.183.109; helo=cp6.superior-host.com;
dkim-signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
 d=kiramek.com	; s=default;
	h=Content-transfer-encoding:Content-type:Mime-version:Message-ID
	:To:From:Subject:Date:Sender:Reply-To:Cc:Content-ID:Content-Description:
	Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:
	In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe:
	List-Post:List-Owner:List-Archive;
	bh=kLzH+E9kPidems+QfUwyA/6rUpiiFy44F1yBJTT915Y=;
	b=YxDoaeYGJZlAeb0pX5mlJEorke
	THQ8IcgLYUrWNhvuKyLRt6BtHuw33HQMb4N/g95lWqVUxVpLxFiYA63DB28EowviCzLUh0bbCn58N
	3VWiGMdlmUVJhMIjorx+g/gCOnhP16wGNtZLSm/HuLpHispbZPu/1/wQvhBWuwI3+8tE532DVPMS1
	n9WHGXhjsfbir4XvaFq+6mL3oodSHWH8wei4CGghY6u2aiChMLCXuzn/hiieIMNvbpHGzrfEeSB5A
	tZu2sZLKxh+UEh5sRKeW7XpWTG1oMws9SVfY39zoiBKr+3x0Y2X1rvsnENzVYKphHfjgvfi0Wwu1x
	ZGM13mNg==;
authentication-results: spf=pass (sender IP is 72.52.183.109)
	smtp.mailfrom=kiramek.com; mit.edu; dkim=pass (signature was verified)
	header.d=kiramek.com;mit.edu; dmarc=bestguesspass action=none
	header.from=kiramek.com;
user-agent: Microsoft-MacOutlook/16.42.20101102
errors-to: piclist-bounces@mit.edu
list-id: "Microcontroller discussion list - Public." <piclist.mit.edu>
list-post: <mailto:piclist@mit.edu>
x-beenthere: piclist@mit.edu
x-mailman-version: 2.1.6
x-source-args:
x-source-dir:
x-antiabuse: Sender Address Domain - kiramek.com
x-source:
x-authenticated-sender: cp6.superior-host.com: james@kiramek.com
x-topics: [PIC]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

madscientistatlarge,

Thank you for your advice regarding the RS-485 interface we have been discu=
ssing.

You suggested the device might require pairing. The "amp" and "Display" don=
't pair insofar as both are housed in the same 2DIN sized head unit and can=
not be separated, so I believe you must have been talking about "pairing ex=
ternally attached devices via the RS-485 lines."  Since I've not been succe=
ssful in getting Toyota dealership techs to reveal any info on that point, =
I can only say that when the small interface board is attached to a third p=
arty automotive CD/DVD player, the factory "Display Audio" head unit immedi=
ately recognizes that player as per the on-screen display of a "DVD button"=
 which normally is not present. =20

In fact, simply connecting the interface PCB to the Display Audio RS-485 wi=
res, without any CD/DVD unit attached at all, will also result in the displ=
ay of that "DVD button" on-screen.  So if there was indeed some kind of "pa=
iring" requirement (like there is when adding a Bluetooth device to an iPho=
ne), I wouldn't expect the "DVD button" to simply appear on the display wit=
h my having done nothing other than just connect that interface PCB.  Would=
 you agree?

As to reading the PIC, I tried that.  It appears to be Code Protected becau=
se Reading the Device Memory shows every Opcode to be 0000 (NOP). All Confi=
g Bits read show a Value of 00.	I used MPLAB IDE 5.25 (MacOS), my PM3, and =
the appropriate wires in the 14-pin header attached to the PIC18F25K80's Vd=
d, Vss, Vpp, CLK & DAT pins.

Once again, here are the data recordings I made to a Saleae logic converter=
:
https://kiramek.com/21test95/Logic_Analyzer_Samples.zip

Free Logic version 1.2.26 (for Windows or Mac or Linux) here:
https://support.saleae.com/logic-software/legacy-software/older-software-re=
leases#logic-1-x-download-links

In order to view both data recording files at once, side-by-side, I downloa=
ded version 1.2.26 of Logic and an older version, which allows me to have t=
wo instances of the app running at once on my Mac, which is the only way to=
 do it since one instance of Logic will only show one data file at a time.

Keep in mind that the 100MHz recording was on the RS-485 wire pair, but the=
 50MHz recording was on the PIC side of the RS-485 IC, hence 4 signals inst=
ead of 2.  But putting both data files on top of eachother and zooming to t=
he same level shows quite similar signals (if you ignore CH0).  CH0 (in bot=
h data files) is the data coming from the factory Display Audio head unit. =
=20

But even though CH1 data (coming from the PIC) is largely the same in both =
data recordings, there are some small differences here and there when you z=
oom in.  Even so, toward the end of both data recording files, you can see =
that I am doing nothing (not touching anything) and the PIC on the interfac=
e board is sending the same exact data stream about once a second, probably=
 to tell the Display Audio unit "I'm still here!"

I have not yet tried sending my own data to the car's head unit because I'm=
 still trying to figure out what this interface PCB is doing.

Best,

James


--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.