Opening a communications port

Comfunc

Return values       (TRUE <> 0, FALSE = 0)

BAUD

Port Baud Rate (9600, 14400, 19200, etc).  See notes below.

BREAK

TRUE/FALSE Break is asserted.  Break is generally used to "get the attention" of the connected modem, terminal or system.

BYTE

Number of bits per byte (4, 5, 6, 7, or 8).

CD

TRUE/FALSE Carrier Detect state.  Synonym for RLSD (READ-ONLY).  When CD is TRUE, the DCE (modem) has a suitable connection on the communications channel present.  When CD is FALSE, there is no suitable connection.

CTSFLOW

TRUE/FALSE Enable CTS output flow control (Input signal).  When CTSFLOW is enabled, it causes the DTE (computer) to stop sending data whenever the CTS signal is set to logic low by the DCE (modem).  Transmission continues when the DCE (modem) sets the CTS signal back to logic high.  The CTS signal is usually used in response to an RTS signal.

DSRFLOW

TRUE/FALSE Enable DSR output flow control (Input signal).  When DSRFLOW is enabled, it causes the DTE (computer) to stop sending data whenever the DSR signal is set to logic low by the DCE (modem).  Transmission is enabled when the DSR signal returns to logic high.  The DSR signal is often used in conjunction with CTS in response to a RTS signal.

DSRSENS

TRUE/FALSE Enable DSR sensitivity.  When DSRSENS is enabled, data received by the DTE (computer) is placed into the receive buffer only if DSR is set to logic high.  If DSR is set low, received data is discarded.  Enabling DSRSENS allows DSR to enable or disable the DTE (the computer) to receive data from the DTE (the modem).  DSRSENS is rarely used in practical communications situations.

DTRFLOW

TRUE/FALSE Enable DTR handshaking flow control (Output signal).  When DTRFLOW is enabled, it signals that the DCE (modem) should prepare to connect to the communications channel.  DTR is usually used for modem on-hook/off-hook control, but can also be used in conjunction with DSR for handshaking.

DTRLINE

TRUE/FALSE Enable DTR line.  When enabled, DTRLINE leaves the DTR line active when the port is closed by the DTE (computer).  This ensures that the DCE (modem) does not close the communications channel when the port is closed.

NULL

TRUE/FALSE Null ($NUL) bytes are discarded when read.

PARITY

TRUE/FALSE Enable parity checking.  This mode must be enabled for the other Parity options to be selected.

PARITYCHAR

Character to use for parity error replacement.  PARITY must be enabled.

PARITYREPL

TRUE/FALSE Enable character replacement on parity error.  PARITY must be enabled.

PARITYTYPE

0 = None, 1 = Odd, 2 = Even, 3 = Mark, 4 = Space.  PARITY must be enabled.  Default = 0.

RING

TRUE/FALSE Ring indicator is on (READ-ONLY).  When RING returns TRUE, a ringing signal is being received on the communications channel (by the modem).  RING approximates the state of the ringing signal; however, it may not report accurately in all Windows platforms.

RLSD

Receive-line-signal-detect (READ-ONLY).  See CD/Carrier Detect above.

RTSFLOW

Ready To Send (Output signal).  0 = Disable, 1 = Enable, 2 = Handshake, 3 = Toggle.  Toggle is used for half-duplex (2-wire) operations to "reverse" the line.  While the DTE (computer) is busy sending data, it raises the RTS signal, and the DCE (modem) blocks its data receive channel.  When RTS signal reverts to logic low, the DCE (modem) reverts to transmit mode and the DTE (computer) switches to receive mode.

Handshake

mode causes the DTE (computer) to check the receive buffer (RXQUE) after each character is placed into the buffer.  When the buffer is 5/6th full, the RTS signal is dropped.  When the receive buffer drops to below 1/6th full, RTS is raised again.

RXBUFFER

Size of the receive buffer in bytes.

RXQUE

Bytes currently in the receive buffer (READ-ONLY).

STOP

0 = 1 stop bits, 1 = 1.5 stop bits, 2 = 2 stop bits.

TXBUFFER

Size of the transmit buffer in bytes.  In some cases, Windows may not be able to report the transmit size.

TXQUE

Bytes currently in the transmit buffer (READ-ONLY).

XINPFLOW

TRUE/FALSE Enable XON/XOFF input flow control.  When the DTE (computer) receive buffer is full, an XOFF character is sent to the DCE (modem) to instruct it to halt transmission.  When the DCE is ready to resume transmission, an XON character is sent to the DCE.  Typically, XOFF is sent when the receive buffer has less than 1/16th remaining, and XON is sent when the receive buffer drops to less than 1/16th of its maximum size.  Default = FALSE.

XOUTFLOW

TRUE/FALSE Enable XON/XOFF out flow control.  When enabled, the DCE (modem) sends an XOFF to the DTE (computer) to halt data transmission to the DCE.  When the DCE is ready to receive more data, an XON character is sent.  XOUTFLOW typically uses the same 1/16th rules as XINPFLOW.  Default = FALSE.