Table of Contents
Advertisement
3. Description of functions
The PW250 is a transparent Level Converter from several interfaces to M-Bus for up to 250 meters. The
device allows external connected controllers such as a building control, a DDC or a PC to read the connected
meters by use of an M-Bus software (not in scope of delivery). The PW250 can also be used as a Repeater
for extension of M-Bus networks relating to the cable length and number of meters.
3.1 Interface multiplexer / switch
An internal microcontroller handles the bus control to just give one interface access to the M-Bus even with
multiple connected interfaces. This ensures that systems do not interfere with each other during the
communication, when two or more systems are connected, for example a BMS via RS485 and a PC via USB.
This automatic switch operates on the principle "first come, first served", i.e. when an interface sends a signal
to the M-Bus, this interface takes control of the M-Bus and has exclusive access to communication. The
"ACTIVE" labeled LED indicates the activity status of the internal interface switch. While the LED is lit, one of
the six possible interfaces is active. The other interfaces are disabled at this time and cannot access the M-
Bus. The active interface remains enabled about 3 seconds after the last communication. Another interface
can occupy the M-Bus as soon as the LED goes off.
3.2 RS232C interfaces
The PW250 has two independent RS232C interfaces, one of them as a 9-pin D-SUB socket in the case front
and the other as a 3-pin screw terminal in the terminal compartment. The RS232C pins assignments are:
RX = PC transmits to M-Bus, TX = PC receives from M-Bus, GND = Signal ground
The pin assignments of the D-SUB socket (female) are designed so that for connection to a PC a simple 9-
pin extension cable (male / female with 1: 1 connection) can be used.
PW250 · User Manual Version 1.1 – 11 / 2019
Pin 1
DCD (data carrier detect)
Pin 2
RXD (PC receives data)
Pin 3
TXD (PC transmits data)
Pin 4
DTR (data terminal ready)
Pin 5
GND (Signal ground)
Pin 6
DSR (date set ready)
Pin 7
RTS (request to send)
Pin 8
CTS (clear to send)
Pin 9
RI (ring indicator)
Unused
M-Bus transmits data to PC
PC transmits data to M-Bus
Bridged to Pin 6 (DSR)
GND
Bridged to Pin 4 (DTR)
Bridged to Pin 8 (CTS)
Bridged to Pin 7 (RTS)
Unused
PW250
6
Advertisement
Table of Contents
