Open Com
Opens a serial port for input and output
Syntax
`
Declare Function Open Com ( byref options As String, As filenumber As Long ) As Long
`
Usage
`
result = Open Com( options[,] As[#] filenumber )
`
Parameters
`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`.
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.
Platform Differences

- On the Windows platform `"COM:"` maps to `"COM1:"`
- 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

- 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`.
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:"`
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.

See also

- `Open`