From: Mike Rigby-Jones <pic.developer@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sat, 4 Jan 2020 23:35:12 -0800
Subject: Re: [EE] MCP2551 CANbus driver behaviour
Thread-Topic: [EE] MCP2551 CANbus driver behaviour
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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 the
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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