From: Neil <picdude3@narwani.org>
To: "piclist@mit.edu" <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Sun, 24 Jan 2021 09:44:44 -0800
Subject: Re: [PIC] PIC18F I2C Start/Stop condition detection
Thread-Topic: [PIC] PIC18F I2C Start/Stop condition detection
Thread-Index: AdbyejfxUrdqAqkqRLKQDw/m7n3YcQ==
Message-ID: <600DB20C.1090901@narwani.org>
References: <600D0BC7.20406@narwani.org>
	<CABTh0a2fy1sJxR32Cn-_3WHdkA5JJEcK6TvFLu2UXKbx8qz+4w@mail.gmail.com>
In-Reply-To:
 <CABTh0a2fy1sJxR32Cn-_3WHdkA5JJEcK6TvFLu2UXKbx8qz+4w@mail.gmail.com>
Reply-To: Microcontroller discussion list - Public. <piclist@mit.edu>
Accept-Language: en-US
X-MS-Exchange-Organization-SenderIdResult: Pass
X-MS-Exchange-Organization-PRD: mit.edu
X-MS-TNEF-Correlator:
received-spf: None (protection.outlook.com: narwani.org does not designate
	permitted sender hosts)
dkim-signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
 d=narwani.org	; s=default;
	h=Content-Transfer-Encoding:Content-Type:In-Reply-To:
	MIME-Version:Date:Message-ID:From:Reply-To:To:References:Subject:Sender:Cc:
	Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender:
	Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:
	List-Subscribe:List-Post:List-Owner:List-Archive;
	bh=soFkL5LQus7hUHksFi6njwfOmTDJ5WhTQYKHPf3D8CY=;
	b=rkz9658mu00cbPq+XMygbhlqeC
	6c4Vod6OWwsu9y5xAT5RtVsBBLhU5fwH5Byry1N2wvvIlGWs7TKtkyLtatGzdPOVe3v2mJPsCn/su
	3oqFbsm890/LpAcktxWVjQc4AMvBspfzVWyXipp3V+fePz7k+wvDr+C29ij87+X4wwFrEy5aRkukB
	S0wdrC9vuhe9t+MLMaGINIDRHB9jDohfIp+i+n3ifcdVw5voYHh6YZXtQsIU+MrbQ68iefEWiBhZh
	jEDYO+BddLykF3nV+8Q6pfWHhT0u8zlvThHQutSeEFEGIIWnZy9yL625N9LxTDaKcrTuOQaH5Y14C
	QaZ5E95A==;
authentication-results: spf=none (sender IP is 68.65.123.242)
	smtp.mailfrom=narwani.org; mit.edu; dkim=pass (signature was verified)
	header.d=narwani.org;mit.edu; dmarc=bestguesspass action=none
	header.from=narwani.org;
user-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101
	Thunderbird/38.5.0
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 - narwani.org
x-source:
x-authenticated-sender: premium47.web-hosting.com: ca4@narwani.org
x-topics: [PIC]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

Joep,

I was looking at fig 26-15, because I was not using AHEN & DHEN.
Even with the behaviour shown in fig 26-17,  I was wondering why=20
clearing this flag would not work, but I just this minute realized (from=20
the SSPxSTAT register definition in fig 26.9.1) that the P and S bits=20
are read-only.  So this explains why my code detects the S bit every=20
time I receive a byte in the ISR.
I'm not sure now how they expect this feature to be used.  My thought=20
was that I'd detect the S bit, initialize my receiving buffer, capture=20
bytes, then when I detect the P bit, verify the recipient (slave address=20
in first byte) is my device and send off the bytes for processing in=20
non-ISR code.
I guess I could check for a change from P to S and S to P to get those=20
transition points, but it's really not an issue, oh well.

Cheers,
-Neil.



On 1/24/2021 2:50 AM, Joep Suijs wrote:
> Neil,
>
> When looking at fig 26-17, it seems S remains high until stop is received=
..
> The description mentions 'detected last', which -although not very specif=
ic
> - might confirm that it remains high until a stop condition is detected.
>
> Joep
>
> Op zo 24 jan. 2021 om 06:59 schreef Neil <picdude3@narwani.org>:
>
>> Hi all,
>>
>> I'm using I2C in slave mode on a PIC18F24Q10.  The incoming packets are
>> like this...
>> http://orlandorobotbuilders.com/stuff/WD-I2C-hold-packet-01.gif
>>
>> The PIC18F24Q10 datasheet is here...
>>
>> https://ww1.microchip.com/downloads/en/DeviceDoc/PIC18F24-25-Q10-Data-Sh=
eet-40001945D.pdf
>>
>> The MSSP has a flag and interrupt for Start and Stop condition (S & P
>> bits in SSPxSTAT) and I tried this code in the ISR to detect these...
>>
>>       if (SSP1STATbits.S =3D=3D 1)
>>       {
>>           TX1REG =3D 'S';
>>           SSP1STATbits.S =3D 0;
>>       }
>>
>>       if (SSP1STATbits.P =3D=3D 1)
>>       {
>>           TX1REG =3D 'P';
>>           SSP1STATbits.P =3D 0;
>>       }
>>
>> (I'm using EUSART1 for debugging to a serial terminal).
>>
>> But I'm getting the 'S' 6 times for each message, and It's repeating the
>> 'P' several times, even after the message is over.  (The package is
>> being sent once only).  Am I missing something obvious here?
>> BTW, I've worked around this already, but just want to know now.
>>
>> Cheers,
>> -Neil.
>>
>>
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>>

--=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
.