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TMCM-6110 Hardware Manual (V1.10 / 2012-JAN-25) 13

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-6110 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 RS-485 electrical interface standard (EIA-485) allows up to 32 nodes to be connected to a single

bus. The bus transceiver used on the TMCM-6110 units (SN65HVD3082ED) has just 1/8th of the standard

bus load and allows a maximum of 256 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 as 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).

node

n - 1

node

Slave Slave

termination

resistor

(120 Ohm)

+5V

GND

pull-up (1k)

pull-down (1k)

RS485- / RS485B

RS485+ / RS485A

Figure 4.6: RS485 bus lines with resistor network

4.5.2 CAN

For remote control and communication with a host system the TMCM-6110 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.

c:>

node

- 1

node

Host

Slave Slave Slave

CAN

termination

resistor

(120 Ohm)

termination

resistor

(120 Ohm)

}

keep distance as

short as possible

Figure 4.7: CAN bus structure