[Hampshire] Raspberry Pi, RS485 and libmodbus

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Author: Roger Munford
To: Hampshire
Subject: [Hampshire] Raspberry Pi, RS485 and libmodbus
I am trying to connect an energy monitor to a raspberry pi equipped with
a small RS485 card from AB electronics. Effectively the card is just an
interface chip between the pi's GPIO pins and the RS485 bus which is
just 3 wires.

I have installed libmodbus and followed the instructions to disable the
serial port login.

Originally I was working with the Bluetooth equipped RP3 but reverted to
RP2 running wheezy because bluetooth complicates things and I thought I
would avoid it.

If anybody is familiar with this sort of setup and may have possibly
come up against the following problem I would be grateful.

I have done the "make check" which tests the libmodbus installation. I
have modified the "test" programme for my environment and the
initialisation and connection are OK but when I try to read the
registers, I get a timeout. The fault could be anywhere.



nd connect correc

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