Open Comfunction

Opens a serial port for input and output, using it as if it were file operations.

Syntax

Declare Function Open Com ( byref options As String, As filenumber As Long ) As Long

Parameters

Name		Description
`options`		A String containing options used in controlling the port.
`filenumber`		The file number to bind to the port.

Return value

Open Com() returns a 32 bit Long: a zero (0) on success and a non-zero error code otherwise.

Description

This command opens a serial port of the PC, allowing to send and receive data by using the normal file commands as Print #, Input #, Get #, ...

The main parameter is a String that describes, at the very least, which communications port to open. It has the format:

"Comn: [ baudrate ][ , [ parity ][ , [ data_bits ][ , [ stop_bits ][ , [ extended_options ]]]]]"

where,
n

Com port to open. "1", "2", "3", "4", etc. Some platforms will support more serial ports depending on how the operating system is configured. Where n is not given, "COM:" will map to "COM1:", except on Linux where "COM:" maps to "/dev/modem"

baudrate

"300" (default), "1200", ..., etc.

parity

"N" (none), "E" (even, default), "O" (odd), "S" (space), "M" (mark), "PE" (QB-quirk: checked, even parity)

data_bits

"5", "6", "7" (default) or "8".

stop_bits

"1", "1.5" or "2". (default value depends on baud rate and data bits, see table below)

Condition	Default number of stop bits
baud rate <= 110 and data bits = 5	1.5
baud rate <= 110 and data bits >= 6	2
baud rate > 110	1

extended_options

Miscellaneous options. (See table below)

Option	Action
'CSn'	Set the CTS duration (in ms) (n>=0), 0 = turn off, default = 1000
'DSn'	Set the DSR duration (in ms) (n>=0), 0 = turn off, default = 1000
'CDn'	Set the Carrier Detect duration (in ms) (n>=0), 0 = turn off
'OPn'	Set the 'Open Timeout' (in ms) (n>=0), 0 = turn off
'TBn'	Set the 'Transmit Buffer' size (n>=0), 0 = default, depends on platform
'RBn'	Set the 'Receive Buffer' size (n>=0), 0 = default, depends on platform
'RS'	Suppress RTS detection
'LF'	Communicate in ASCII mode (add LF to every CR) - Win32 doesn't support this one
'ASC'	same as 'LF'
'BIN'	The opposite of LF and it'll always work
'PE'	Enable 'Parity' check
'DT'	Keep DTR enabled after CLOSE
'FE'	Discard invalid character on error
'ME'	Ignore all errors
'IRn'	IRQ number for COM (only supported (?) on DOS)

All items except for the COM port are optional. The order of baudrate, parity, data_bits, stop_bits is fixed. Any skipped fixed item ( baudrate, etc...) must be empty.

The error code returned by Open Com can be checked using Err in the next line. The function version of Open Com returns directly the error code as a 32 bit Long.

Remarks

Usage



result = Open Com( options[,] As[#] filenumber )

Platform Differences

On the Windows platform

"COM:" maps to "COM1:"
baud rate must be an unsigned 32-bit integer, and is passed on directly to the operating system.

On the Linux platform

"COM:" maps to "/dev/modem"
"COM1:" maps to "/dev/ttyS0"
"COM2:" maps to "/dev/ttyS1", etc
"/dev/xyz:" maps to "/dev/xyz", etc
baud rate must be one of 50, 150, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 500000, 576000, 921600, 1000000, 1152000
in fbc >= 1.09.0, baud rate can also be one of 1500000, 2000000, 2500000, 3000000, 3500000, 4000000
the baud rates supported depend on the system where the fbc compiler itself was compiled and built

The DOS serial driver is experimental and can access COM ports 1 to 4

It uses the following base io and IRQ's as default:
COM1 - &h3f8 - IRQ4
COM2 - &h2f8 - IRQ3
COM3 - &h3e8 - IRQ4
COM4 - &h2e8 - IRQ3
An alternate IRQ can be specified using the the "IRn" protocol option where n is 3 through 7 (first PIC). Since fbc 1.10.0, n can also be 8 through 15 (second PIC).
Currently not supported: IRQ's on the slave PIC, alternate base I/O addresses, Timeouts and most errors as detected in QB, hardware flow control, FIFO's.
"COM:" maps to "COM1:"
baud rate must be between 50 and 115200

Dialect Differences

In the -lang qb dialect the old syntax OPEN "COMx:... is supported.

Differences from QB

In QB the syntax was OPEN "COMx:[baudrate] [,parity, [data_bits, [stop_bits, [extended_options]]]]" FOR INPUT|OUTPUT|RANDOM AS [#] n
In QB, only "COM1:" and "COM2:" are supported. In FreeBASIC, any correctly configured serial port may be used.

Example

Open Com "COM1:9600,N,,2" As 1
Opens COM1 with 9600 baud, no parity, 7 data bits and 2 stop bits.

Open Com "COM1:115200" As 1
Opens COM1 with 115200 baud, "even" parity, 7 data bits and 1 stop bits.

Reference

Documented in KeyPgOpenCom.html