Interfaces and Connectors
EPM-32 Reference Manual
29
Serial Ports
The EPM-32 features two on-board 16550-based serial channels located at standard PC I/O
addresses. COM1 is an RS-232 (115.2K baud) serial port. The IRQ line is chosen in CMOS
Setup.
COM2 can be operated in RS-232, 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. The IRQ line
is chosen in CMOS Setup.
Each COM port can be independently enabled or disabled in the CMOS setup screen.
These ports use IEC 61000-4-2-rated TVS components to help protect against ESD damage.
COM
P
ORT
C
ONFIGURATION
There is no configuration jumper for COM1 since it only operates in RS-232 mode.
Use CMOS Setup to select between RS-232/RS-422/RS485 operating modes for COM2.
Jumper V1[7-8] is used to enable the RS-422/485 termination resistor for COM2. The
termination resistor should be enabled for RS-422 and the RS-485 endpoint station. It should be
disabled for RS-232 and the RS-485 intermediate station.
COM2
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 COMDIR
bit in offset 0 of the Special Control Register. See page 47.
The following code example shows how to toggle the line driver for COM2 when the base
address for the Board Control Registers (BCRs) is set to 1D0h.
MOV DX,1D0H ; POINT TO SPECIAL CONTROL REGISTER
IN AL,DX ; FETCH EXISTING VALUE
OR
AL,08H ; SET BIT D3, COMDIR
OUT
DX,AL ; WRITE MODIFIED VALUE