Serial Port Status line of the MonTel Server

The Serial Port Status line contains information about the Serial Port and the Serial Port buffer. It is found on the Server Console Screen above the error messages.

Buffer

The size of the buffer is monitored and the number of characters present shown in brackets (left padded with zeros). (A buffer is a temporary storage of data so that we can finish what we are doing before we have to deal with it). This is the Buffer inside MonTel, and NOT the buffer inside either the operating system or the hardware. In the case of the Console Version of MonTel, the Serial Port is buffered first by the Hardware, then By Windows or the Windows Driver, Read by a separate thread, and stored in the MonTel Server Buffer. It is the state of the this last buffer that is shown here.

Because of these layers of buffering, it is possible that the MonTel Server may have signalled that its buffer is full, and that the serial port is off, when it is in fact still receiving data (and buffering it in the operating system driver).

At the time this topic was written the MonTel Server used an 8k buffer, which is enough to hold about 100 (typical) call records worth of data.

Com Port

The state of the relevant Asynchronous communications (serial) port used by MonTel is shown. The On or Off shows if MonTel is currently reading characters from the buffer (on means yes). In DOS systems the Com port must be COM1, 2 3 or 4. In Windows systems the COM port may have other names depending on the driver used.

Com Port Status and Errors

After the Colon, the COM port displays the status of the COM Port. Due to the over heads of keeping up with this information directly MonTel may lag a little, showing changes in the status for a second rather than instantaneously. This also makes it a lot more readable!

What do the fields mean? (Delta means change.)

E_FIFO:	At least one error is pending in the receive First In First Out Hardware buffer.
E_TEMT:	Transmitter Empty (last word has been sent). This field is no longer displayed by MonTel.
THRE:	Transmitter Holding Register Empty (new data can be written to THR). This field is no longer displayed by MonTel. It used to be called THREMPTY.
BRK:	Broken line detected. (May mean either - a three wire cable is being used, or the cable has been removed from the computer).
E_FE:	Framing Error.
E_PE:	Parity Error.
E_OE:	Overrun Error.
E_RBF:	Receiver Buffer Full (Data Available)
DCD:	Data Carrier Detect. (Hand shaking line). This settings is sometimes called RLSD (receive-line-signal-detect). The Windows API uses this nomenclature. Elsewhere it is called CD for just Carrier Detect.
RI:	Ring Indicator. (Very unlikely to be seen!!!)
DSR:	Data Set Ready. (Hand shaking line)
CTS:	Clear To Send. (Hand shaking line)
D_DCD:	Delta Data Carrier Detect (Change in Hand shaking line in the last second.)
D_RI:	Delta Ring Indicator (Trailing Edge and Very unlikely to be seen!!!))
D_DSR:	Delta Data Set Ready (Change in Hand shaking line in the last second.)
D_CTS:	Delta Clear To Send (Change in Hand shaking line in the last second.)

Bibliography

• ftp://ftp.phil.uni-sb.de/pub/staff/chris/The_Serial_Port, by Christian Blum
• Serial Communications in Win32, by Allen Denver Microsoft Windows Developer Support