Farnell TRC-8543, Руководство пользователя

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This configuration allows the NXP fault-tolerant CAN transceiver to detect and
recover from bus faults. It is important to determine the overall termination of the
existing network, or the termination of the individual device, before connecting it to
a low-speed/fault-tolerant port. NXP recommends an overall RTH and RTL
termination of 100 Ω to 500 Ω (each) for a properly terminated low-speed network.
You can determine the overall network termination as follows:
1
R
RTHoverall
=
1
R
RTHnode1
+
1
R
RTHnode2
+
1
R
RTHnode3
+
1
R
RTHnoden
NXP also recommends an individual device RTH and RTL termination of 500 Ω to
16 kΩ. After determining the existing network or device termination, you can use the
following formula to indicate which nearest value the termination property needs to
be set to produce the proper overall RTH and RTL termination of 100 Ω to 500 Ω
upon connection of the card:
where R
RTH overall
should be 100 Ω to 500 Ω
NI-XNET Low-Speed/Fault-Tolerant CAN hardware features software selectable bus
termination resistors, allowing you to adjust the overall network termination
through an API call. In general, if the existing network has an overall network
termination of 125 Ω or less, you should select the 5 kΩ option for your NI-XNET
device. For existing overall network termination above 125 Ω, you should select the
1 kΩ termination option for your NI-XNET device.
Onboard termination on the low-speed/fault-tolerant ports of the TRC-8543 is set
through the NI-XNET software to either 1.11 kΩ or 4.99 kΩ.
Cable Lengths
The cabling characteristics and desired bit transmission rates affect the allowable
cable length. You can find detailed cable length recommendations in the ISO 11898,
CiA DS 102, and DeviceNet specifications.
ISO 11898 specifies 40 m total cable length with a maximum stub length of 0.3 m for
a bit rate of 1 Mb/s. The ISO 11898 specification says that significantly longer cable
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TRC-8543