
Interfaces and Connectors
EBX-18 Hardware Reference manual
30
Serial Ports
The EBX-18 includes four on-board 16550-based serial channels located at standard PC I/O
addresses. Each COM port can be independently enabled or disabled in BIOS Setup.
All four COM ports by default are set to RS-232 mode
COM1 and COM2 are RS-232 (115.2K baud) serial ports. There are no configuration
jumpers for COM1 and COM2 because they only operate in RS-232 mode. IRQ lines are
chosen in the BIOS Setup program.
COM3 and COM4 can be operated in RS-232 or RS-422/485 mode. IRQ lines are chosen in
the BIOS Setup program.
Additional non-standard baud rates are also available through the BIOS Setup program.
COM3/COM4
H
ARDWARE
C
ONFIGURATION
Jumper block V1[3-4] enables the RS-422/485 termination resistor for COM3. Jumper V1[7-8]
enables the RS-422/485 termination resistor for COM4. The termination resistor should be
enabled for an RS-422 endpoint station; it should be disabled for RS-232 and RS-485 non-
endpoint receivers.
Table 16: COM3/COM4 Control and Termination Jumpers
Jumper
Position
Function
Jumper In
Jumper Out
1-2
Use RTS#/DE for COM3
RS-232/485 (default)
RS-422
3-4
COM3 Rx End-point Termination
RS422/485 (
Note
)
RS-232 (default)
5-6
Use RST#/DE for COM4
RS-232/485 (default)
RS-422
7-8
COM4 Rx End-point Termination
RS422/485 (
Note
)
RS-232 (default)
Note:
RS-485 non-endpoints do not require termination. If receivers are mid-line, remove this termination jumper.
Figure 14. COM3/COM4 Control and Termination Jumpers