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Chapter 3: Software Installation - DOS
Echo
User's Manual, ver. 0.00
Character Device Access
Character device access provides a "high level" interface which
is appropriate for simple applications and tests. Each port is
given a device name which you can access similar to a file. The
device name is formed by concatenating the port number to the
name (
COM
if not specified by the
D=
command ). For example, if
two ports are installed with the parameter
N=2
, then the device
names will be
COM2
and
COM3
.
Some programming languages will assume that access to
COMn
is
limited to the number of communication ports supported by the
computers BIOS. To avoid this problem, the name can be
changed. If two ports are installed with the parameters
D=SERIAL
the names will be
SERIAL1
and
SERIAL2
. In this case, the
N=
parameter is not added to the number of the name.
INT 14h Access
The DFlex DOS driver provides the standard four INT 14h
functions for the additional ports supported. To interface to these
functions, DX is set to the port number minus 1. If the
N=
parameter has been specified, this value must be added into the
DX to skip the standard ports.
