
Serial Ports
Serial Ports
The
EPM-CPU-10
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.
COM2 can be operated in RS-232, RS-422, or RS-485 modes. Two additional non-standard baud
rates are also available (programmable in the normal baud rate registers) of 230K and 460K baud.
Interrupt assignment for each COM port is handled in CMOS Setup, and each port can be
independently enabled or disabled.
COM P
ORT
C
ONFIGURATION
There are no configuration jumpers for COM1 because it only operates in RS-232 mode.
Jumper VS3 is used to configure COM2 for RS-232/422/485 operation. See page 16 and 17 for
jumper configuration details.
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 DTR
handshaking line.
The following code example shows how to turn the line driver for COM2 on and off:
mov dx,02FCh ; Point to COM2 Modem Control register
in al,dx ; Fetch existing value
or
al,01h ; Set bit D0
out
dx,al ; Turn DTR on (enables line driver)
in al,dx ; Fetch existing value
and al,0FEh ; Clear bit D0
out dx,al ; Turn DTR off (disables line driver)
EPM-CPU-10 Reference Manual
Reference – 25