From: Neil <picdude3@narwani.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 5 Jan 2020 05:47:46 -0800
Subject: Re: [EE] MCP2551 CANbus driver behaviour
Thread-Topic: [EE] MCP2551 CANbus driver behaviour
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Ahhh... missed that.  Thanks!




On 1/5/2020 2:35 AM, Mike Rigby-Jones wrote:
> Look at section 1.5 TXD Permanent Dominant Detection. The driver will
> disable outputs if you hold a low state for more than 1.25ms to protect t=
he
> CAN bus.
>
> Regards
>
> Mike
>
> On Sun, 5 Jan 2020, 06:42 Neil, <picdude3@narwani.org> wrote:
>
>> Hi,
>>
>> Tinkering with an MCP2551 CAN driver chip on a breadboard and the
>> behaviour is not what I expect...
>> First, I've got 5V and ground to Vdd and Vss resp., a 20k resistor on Rs
>> to ground, and a 120-ohm resistor across CANH and CANL.
>> Second, the datasheet is here...
>> http://ww1.microchip.com/downloads/en/DeviceDoc/20001667G.pdf
>>
>> Table 1-2 (truth table) says that I should get a differential voltage
>> (~2V as per CAN spec) when TXD is low, and I expect that it will be
>> continuous, but I get a spike for a few ms (haven't actually measured
>> the time)
>>
>> What an I missing or misinterpreting here?
>>
>> Cheers,
>> -Neil.
>>
>>
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