EPM-15 Reference Manual
27
Interfaces and Connectors
Serial Ports
The EPM-15 features three on-board 16550-based serial channels located at standard PC I/O
addresses. Connector J8 provides interfaces to the COM ports. See Table 6 for COM port signal
and pinout information.
COM1 is an RS-232 (115.2K baud) serial port. COM3 and COM4 can be operated in RS-422 or
RS-485 modes. Additional non-standard baud rates are also available (programmable in the
normal baud registers) of up to 460K baud.
Interrupt assignment for each COM port is handled in CMOS Setup, and each port can be
independently enabled or disabled.
Note:
If a COM port is disabled in CMOS Setup, its I/O address space is available to the
PC/104 (ISA) bus.
All serial ports are protected against ESD damage. This protection exceeds the 15KV human
body model.
COM
P
ORT
C
ONFIGURATION
There is no configuration jumper for COM1 because it operates only in RS-232 mode.
Jumper blocks V1 (labeled V5 on 3.xx and earlier boards) and V3 are for termination of the RS-
422/485 differential pairs. See Table 3 for details on termination configuration.
COM3
AND
COM4
RS-485
M
ODE
L
INE
D
RIVER
C
ONTROL
The TxD+/TxD– differential line driver can be turned on and off by manipulating the RS-485/422
Transmit/Receive Control Register. Refer to page 44 for more information.
The following code example shows how the BIOS initializes COM3 and COM4 to RS-422 mode:
; set up 485/422 register in pld
mov dx, 1dah ; IO port in PLD
mov al, 33h ; initialize RS-422/485 line drivers to RS-422 mode
out dx, al
5
5
