Communication Ports; Can Interfaces - Novatel OEM6 Series User Manual

E.1.5

Communication Ports

COM1, COM2 and IMUCOM (COM6) present software-selectable RS232 or RS422 signal levels. RTS/
CTS flow control is available on each port. COM1 and IMUCOM are protected to ±15 kV (HBM)
discharges. COM2 is protected to ±26 kV (HBM) discharges. Additional ESD protection is recommended
near the enclosure connectors for any signal leaving an enclosure.
COM3, COM4 and COM5 are 3.3 V CMOS-level signals only. RTS/CTS flow control is available for each
interface but COM2 also has DTR/DCD flow control (for reverse-compatibility with the OEMV-3G
receiver). These signals are 3.3 V CMOS UARTs that require an external transceiver to connect to an
RS232 or RS422 device. These pins have some ESD protection but (again) additional ESD protection
near the connectors for any signals leaving an enclosure is recommended.
A combination of a series ferrite bead and small value shunt capacitor is recommended on any RS232/
RS422 lines that leave the enclosure (similar to the arrangement used on the I/O ports and CAN
interfaces below). (The TVS recommended for 3.3 V CMOS-level I/O is unsuitable for RS232-level I/O.
An additional low capacitance TVS device with a clamping voltage between 18 V and 25 V should be
selected for RS232 lines requiring additional protection.)
E.1.6

CAN Interfaces

The OEM638 provides two CAN ports through the expansion header. The transceivers are provided on
the OEM638. The following figure shows a typical CAN protection and EMI filtering arrangement.
The combination of ferrite beads and small value capacitors are not necessarily required but may provide
improved EMI performance. A low capacitance TVS device is shown on the schematic to provide ESD
protection.
OEM6 Family Installation and Operation User Manual Rev 7 165