68300

I have a CAN application in which I need to provide the option for a fiber
optic output.  I can't use an external converter, it has to be on the board.
Any ideas on how to implement this?  I can't find any "CAN fibre
transceivers", so I am assuming I will have to build one?

-----Original Message-----
From: Godiska, Jim [mailto:jgodiska@...]
Sent: Wednesday, August 28, 2002 8:05 PM
To: '68300@yahoogroups.com'
Subject: RE: [68300] 68376: CAN bus rate and length issue


Jeff,

My sincere thanks for your replies.  I felt I was going in the right
direction, but it is always good to hear confirmation from the experts.

Although I was hoping to avoid it, I do have the option to cut my data rate
in half (to 500 kHz).  At 1 MHz my loading of the bus would be about 15%,
with 500 kHz we would be about 30% for a maximum.  In the early days, I
found that 250 kHz was a definite problem, and I needed something in the 330
kHz range for decent operation.

I do have another questions, though.  If I would end up needing the 1 MHz
data rate and a longer network on a future design, do you have any
suggestions as for how to do this?  I came up with a couple of ideas, but I
do not know how well they would work:

1.  Replace the line tranceiver chip with a fiber optic cable network.

2.  Make up a repeater module using a microcontroller with 2 CAN bus
controller modules to act as a CAN message receiver / buffer /
re-transmitter unit.  But some of the effective data bandwidth will
obviously be limited by the repeater's processing time.

Again, thanks for your help, Jeff.

Jim

-----Original Message-----
From: jeffrey.tenney@... [mailto:jeffrey.tenney@...]
Sent: Wednesday, August 28, 2002 7:54 PM
To: 68300@yahoogroups.com
Subject: Re: [68300] 68376: CAN bus rate and length issue



Jim,

Oops, correction here.  Another difference in your choices for TouCAN
settings is the sample mode, once per bit or three times per bit.  I have
no idea why they even put that option into the TouCAN, but my opinion is
that it's useless.  Pick your sample point (as you've picked 80%) and let
the CAN protocol do the rest.

Jeff



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