QBasic 1.1: OPEN COM Statement

Explanation

OPEN COM Statement

Opens and initializes a communications channel for input or output (I/O). The OPEN COM statement must be executed before a device can be used for communication using an RS232 interface.

Worth knowing

Useful and cross-version information about the programming environments of QBasic, QuickBasic and Visual Basic for DOS.

ASCII Code Tables
Keyboard Scan Codes
Syntax Conventions
Screen Modes
Color Attributes
Error Codes

You are here: References Overview > QBasic 1.1 Commands List > OPEN COM Statement

Syntax

OPEN "COMn: optlist1 optlist2" [FOR mode] AS [#]filenum% [LEN=reclen%]

Description / Parameter(s)

The communications port to open (1 = COM1, 2 = COM2).

optlist1

The most-often-used communications parameters:
 [baud] [,[parity] [,[data] [,[stop]]]]
baud is the baud rate of the device to be opened:
 75, 110, 150, 300, 600, 1200, 2400, 4800, 9600
parity is the method of parity checking:
 N (none)     E (even)    O (odd)
 S (space)    M (mark)    PE (enable error checking)
data is the number of data bits per byte:
 5, 6, 7, 8
stop is the number of stop bits:
 1, 1.5, 2
Defaults: 300 baud, even parity, 7 data bits, 1 stop bit.

optlist2

A list of less-often-used parameters, separated by commas:

Option	Description
ASC	Opens the device in ASCII mode.
BIN	Opens the device in binary mode.
CD[m]	Sets the timeout period (in milliseconds) on the Data Carrier Detect (DCD) line.
CS[m]	Sets the timeout period (in milliseconds) on the Clear to Send (CTS) line.
DS[m]	Sets the timeout period (in milliseconds) on the Data Set Ready (DS) line.
LF	Sends a line-feed character after a carriage return.
OP[m]	Specifies how long (in milliseconds) OPEN COM waits for all communications lines to become open.
RB[n]	Sets the size (in bytes) of the receive buffer.
RS	Suppresses detection of Request to Send (RTS).
TB[n]	Sets the size (in bytes) of the transmit buffer.

mode

INPUT, OUTPUT, or RANDOM (the default). See OPEN Statement File Modes.

filenum%

A number in the range 1 through 255 that identifies the communications channel as long as it is open.

reclen%

Random-access-mode buffer size (default is 128 bytes).

Example


'Use this example for trouble shooting serial communications problems.
'Slow baud, hardware handshaking is ignored and buffers are enlarged.
OPEN "COM1:300,N,8,1,CD0,CS0,DS0,OP0,RS,TB2048,RB2048" FOR RANDOM AS #1