define(`TITLE', `A simple Modbus RTU to TCP gateway')
define(`DATE', `2014-10-27')
define(`CONTENT', `
Meterbus is a great Thing, especially as two-wire slave (bus-powered) are possible. Unfortunately the Meterbus Transceiver TSS721A is rather expensive and not that easy to obtain.

So, I decided to test another fieldbus: Modbus. A Modbus Transceiver (here: LTC485) is much cheaper than the TSS721A and moreover a 1-phase powermeter with Modbus interface is about 30€, a 1-phase powermeter with Meterbus interface is about 90€.

I found some Arduino libraries for both Modbus RTU and Modbus TCP on the Net so I started with a simple Modbus master talking to a 1-phase powermeter:

<a href="http://a385e-5.de/wp-content/uploads/2014/10/IMG_1045.jpg"><img src="http://a385e-5.de/wp-content/uploads/2014/10/IMG_1045-300x225.jpg" alt="IMG_1045" width="300" height="225" class="alignnone size-medium wp-image-506" /></a>

Communication works:

<a href="http://a385e-5.de/wp-content/uploads/2014/10/SCR04.png"><img src="http://a385e-5.de/wp-content/uploads/2014/10/SCR04-300x243.png" alt="SCR04" width="300" height="243" class="alignnone size-medium wp-image-507" /></a>

(Blue and yellow are the Modbus lines, purple is TX at the microcontroller, green is RT at the microcontroller.)
')