TMCM-1160 V1.01 Hardware Manual (Rev. 1.02 / 2013-JUL-23)
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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 transceiver used on the TMCM-1160 units (SN65HVD485ED) has 1/2 of the
standard bus load and allows a maximum of 64 units to be connected to a single RS485 bus.
4. 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. In contrast to the
termination resistors this network is normally required just once per bus. Certain RS485 interface
converters available for PCs already include these additional resistors (e.g. USB-2-485).
Slave
Slave
+5V
node node
n- 1
n
pull-up (1k)
termination
RS485+ / RS485A
RS485- / RS485B
resistor
(120 Ohm)
pull-down (1k)
GND
Figure 3.5 Bus lines with resistor network
3.2.2.2 CAN
For remote control and communication with a host system the TMCM-1160 provides a CAN bus interface.
Please note that the CAN interface is not available in case USB is connected. For proper operation the
following items should be taken into account when setting up a CAN network:
5. BUS STRUCTURE:
The network topology should follow a bus structure as closely as possible. That is, the
connection between each node and the bus itself should be as short as possible. Basically, it
should be short compared to the length of the bus.
Host
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
CAN
Figure 3.6 CAN bus structure
6. 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-1160
does offer on-board termination resistors which can be activated with the help of a jumper (see
chapter 7). The jumper has to be removed for units not connected to one end of the bus!
7. NUMBER OF NODES:
The bus transceiver used on the TMCM-1160 units (TJA1050T or similar) supports at least 110
nodes under optimum conditions. Practically achievable number of nodes per CAN bus highly
depends on bus length (longer bus -> less nodes) and communication speed (higher speed ->
less nodes).
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