SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
2.8.2.2. EMI Protection
An LC filter is frequently used in serial networks to increase system
reliability with respect to EMC.
EMI
emitted from an end serial device
through the RS232/RS422/RS485 transceivers can be filtered, thus
limiting unwanted high-frequency noise on the communication bus.
2.8.2.3. Terminations
A RS422/RS485 bus must be terminated at both ends with a
120 ohm
resistor between the differential signal pair. It is best to always terminate
your bus properly at both ends. This will allow for maximum data integrity
at high and low speeds.
2.8.2.4. Routing Considerations for Serial Interface
See
SMARC T335X
layout guide for trace routing guidelines and the
SMARC
specification for more information about this subject.
2.8.3. Asynchronous Serial Interface Reference Schematic
The example shown below is implemented on the
SMARC T335X
evaluation
carrier board. The RS232, RS322 and RS485 transceivers that used are
from
TI MAX3243
and
SN75HVD11D
that has built-in 16kV
ESD
protection.
A jumper block is also used to select the RS232, RS422 or RS 485 mode.