Dangerous Prototypes

Dangerous Prototypes => Bus Pirate Support => Topic started by: Eddiie on November 11, 2019, 05:51:49 am

Title: Want to listen in on RS485 bus
Post by: Eddiie on November 11, 2019, 05:51:49 am
Hello,

New to BP3.6 a really nice tool to have.   I want to use this to listen in on a RS485 line that uses RX+, RX-,  TX+, TX- for signaling.
How do I accomplish this with the BP?   Should I convert the signals to RS232 before connecting the BP?   Ah, and drop voltage down...  Pretty sure it would be CMOS RS232 levels.. I think 12v.   

Thank you for the assistance!
Title: Re: Want to listen in on RS485 bus
Post by: ian on November 11, 2019, 09:40:13 am
Hello,

You'll need a RS485 to <=5volts output PHY of some kind. Microchip has a few that are easy to use, as I recall.
Title: Re: Want to listen in on RS485 bus
Post by: Eddiie on November 16, 2019, 09:08:03 pm
I guess another approach is to find the communication chip the unit uses (like a Max3491e) and tap into that.  
Meaning, tap into the low voltage side.  The unit does not use those levels on the chip.  It has to go through a series of filters and lower the voltage to 3.3 (or maybe 5) before it can be used.   Look for that and tap in there.

Answered my own question.  :)
Title: Re: Want to listen in on RS485 bus
Post by: ian on November 18, 2019, 10:08:02 am
Also a good approach, and doesn't need extra parts :)

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