Regin Regio Maxi, Manual

Page: 81 / 99

Regio Manual Maxi
Chapter 19
Signal types 81
Modbus wiring etc.
A protocol such as Modbus consists of several layers (OSI-model). The bottom layer
is always the physical layer, number of wires and signal levels. the next layer
describes the communication digits (number of data bits, stop-bits, parity etc). Then
come the layers describing the Modbus specific functions (number of digits per
message, the meaning of different messages etc).
For Modbus, the bottom layer can be RS485, RS422 or RS232.
RS485 contra RS422
RS485 and RS422 are the electric part of the protocol, i. e. the physical layer.
RS485 has two connections, A and B. Often there is also a protecive earth (N on
EXOmodules). RS485 units are always connected A
 A and B  B. RS485 is so
called half duplex communication: Communication can only go in one direction at a
time; i. e. the master will first send an enquiery and will thereafter listen for the reply.
A and B are used for both transmission and reception.
RS422 is a full duplex communication which means you need 4 wires, 2 for transmit
(Tx+ and Tx-) and 2 for receive (Rx+ and Rx-). Tx is used to transmit and Rx to
receive which means that Tx in one unit must be connected to Rx in the other and
vice versa. As for signal levels etc. RS422 and RS485 are identical.
To interconnect RS485 and RS422: On the RS422 unit connect Tx+ with Rx+ and
Tx- with Rx-. We have now changed a 4-wire system to a 2-wire system and can
connect them to A and B on the RS485 unit. Which goes whare is something you
most often need to find out by trial and error. Incorrect polarity will just give nonfunction but
cannot harm either unit.
Tx+ -----|---------------------------------------- A (or B)
|
Rx+ -----|
Tx- -----|---------------------------------------- B (or A)
|
Rx- -----|
Bitrate, two stop bits, parity is the next layer.
These settings must correspond to the settings in the master unit. Find out how the
master is set and then give the Controller the same settings.
Parity can be set to odd, even or none. If none is chosen two stopbits will automatically be
used. If odd or even is chosen only one stop-bit is used otherwise there will be too many bits
altogether: 1 start-bit, 8 data-bits, 1 parity-bit and 1 stop-bit give a total of 11 bits which is
maximum.
LonWorks
Models with LON communication have a communication port for LonWorks. Connection to
the network is established using the programming tool LonMaker. The xif-file is available
for download from Regin’s homepage. Network variables for LON can be found at the end
of chapter 20.