TMCM-3214, TMCM-3215 Hardware Manual (V0.90 / 2016-JUN-27)
Host
19
Slave
node
1
Slave
Slave
c:>
node node
- 1
n
n
}
termination
resistor
termination
resistor
(120 Ohm)
(120 Ohm)
keep distance as
short as possible
RS485
Figure 5.3: Bus structure
2. BUS TERMINATION:
Especially for longer busses and/or multiple nodes connected to the bus and/or high communication
speeds, the bus should be properly terminated at both ends. The TMCM-3214 does not integrate any
termination resistor. Therefore, 120 Ohm termination resistors at both ends of the bus have to be added
externally.
3. NUMBER OF NODES:
The RS485 electrical interface standard (EIA-485) allows up to 32 nodes to be connected to a single bus.
The bus transceivers used on the TMCM-3214 units (SN65HVD1781D) have a significantly reduced bus load
and allow a maximum of 255 units to be connected to a single RS485 bus using TMCL firmware. Please
note: usually it cannot be expected to get reliable communication with the maximum number of nodes
connected to one bus and maximum supported communication speed at the same time. Instead, a
compromise has to be found between bus cable length, communication speed and number of nodes.
4. COMMUNICATION SPEED:
The maximum RS485 communication speed supported by the TMCM-3214 hardware is 1Mbit/s. Factory
default is 9600 bit/s. Please see separate firmware manuals for information regarding other possible
communication speeds below the upper limit in hardware.
5. NO FLOATING BUS LINES:
Avoid floating bus lines while neither the host/master nor one of the slaves along the bus line is
transmitting data (all bus nodes switched to receive mode). Floating bus lines may lead to communication
errors. In order to ensure valid signals on the bus it is recommended to use a resistor network connecting
both bus lines to well defined logic levels.
There are actually two options which can be recommended:
Add resistor (Bias) network on one side of the bus, only (120R termination resistor still at both ends):
Slave
Slave
+5V
pull-up (680R)
termination
node node
n- 1
n
RS485+ / RS485A
RS485- / RS485B
termination
resistor
resistor
(120R)
(220R)
pull-down (680R)
GND
Figure 4.4: Bus lines with resistor (Bias) network on one side, only
Or add resistor (Bias) network at both ends of the bus (like Profibus™ termination):
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
