Common Settings, Serial Ports

The Common Settings apply to all capture channels.  Once these settings have been specified, OK or Apply should be clicked.  This tab defines up to 500 Serial Port capture channels (hardware permitting) that are specified using a grid.

This grid allows different settings to be specified for each different serial RS232 communications port.  If the port is unknown, the Test RS232 Signals utility may be used to find which port has active signal lines. All installed serial COM ports will be displayed, not necessarily contiguously, but only a total of 500 may be captured at once with ComCap Unlimited, or three with ComCap Standard.  Most older PCs will have COM1 and COM2, newer ones only COM1, other serial ports may be available using USB to RS232 serial adapters or PCI expansion cards with multiple RS232 ports.  Note that RS232 serial ports not recognised by the PC BIOS need special windows driver software installed, which is usually supplied with the hardware.  Some virtual ports may have strange names like CNCA2, but these will work identically to those starting with COM.

Virtual serial ports may also be installed by some applications to allow those applications to be accessed by software such as ComCap. If the requirement is to capture serial data from another application on the same PC, ComCap includes a Null Modem Emulator (com0com) from http://com0com.sourceforge.net/ that installs a linked pair of virtual serial ports, instead of needing to use a physical pair of COM ports and a null modem cable.

ComCap has been tested with various serial port expansion products:

To edit the grid, click on the required box and an edit control of some sort will appear, perhaps a drop down box arrow, an edit field or numeric up/down arrows.  Once the edit is complete, click on another box to ensure the edit is saved, losing focus from the grid causes the last edit to be cancelled. 

Capture Name

The Capture Name uniquely identifies this capture channel, and is displayed on the main window tabs and in the information logs.  It may optionally be added to each captured line and may be used as part of the file name for capture logs.  Generally, the name should be as short as possible, while meaningfully describing the purpose of the channel.  The Capture Name defaults to the serial port name.  Note Capture Names must be unique for Network channels as well.

Enabled

The Enabled tick box determines whether this channel will be captured.  If unticked, the channel will not appear in the main window.  It’s typically used to temporarily disable a channel without deleting it.

Port

Displays the port name, from COM1 to COM200, may not be changed.  The COM port is used to identify settings in the configuration files comcap.config and comcap.current, ie [COM1], [COM2], etc. 

Speed

Speed is a drop down list of possible communication speeds for the RS232 data source, ranging from 300 to 256,000 bits per second.  Older PCs may only reliably support speeds up to 9,600 bits/sec.  Actual communication speed is bits per second divided by the bits per character which is typically 10 (1 start bit, 8 data bits, 1 stop bit), so 9,600 bits/sec equals 960 characters per second (about 12 lines).  If random data is being captured, try adjusting the Speed higher or lower.  If there are problems capturing data, sometimes slowing the speed will help, but must be done at the data source as well.

Parity

Parity is a drop down list of possible parity types used by the RS232 data source being captured.  For 8-bit data, parity is usually set to None.  For 7-bit data, there are odd, even, mark and space options (which then total 8 bits).  Rarely, parity is used with 8-bit data.  If the parity is incorrect, some characters may appear incorrectly, typically as foreign characters. 

Data Bits

Data Bits is a drop down list of data bits in the RS232 data source, ranging from 5 to 8 bits per second.  5 and 6 bits are used by telegraph and telex type sources (only upper case letters), 7-bit is ASCII upper and lower, 8-bit also includes foreign characters and special symbols.  7-bit usually has odd or even parity selected as well, 8-bit is normally no parity.

Stop Bits

Stop Bits is a drop down list of the number of stop bits in the RS232 data source, normally 1 bit, but perhaps 2 bits for very slow data.

Xon/Off Flow Control

ComCap normally uses hardware flow control, by setting the RTS and DTR lines high when capture is started and then dropping RTS if no more data can be buffered.  Selecting Xon/Xoff flow control causes xon and xoff symbols to be transmitted when data can be accepted or needs to be stopped.  The size of the download data buffer for each COM port is about 62,000 bytes which is about one minute of data at 9.600 bits/sec, after which flow control should stop new data being received in the rare case that ComCap can not process incoming data in real time.

Control Lines

This option determines whether the three serial control lines CTS, DTS and DCD should be checked during capture, to make detection of connection or hardware problems easier since an alert can be sent if capture stops. If ticked, capture will only start when at least one of the three control lines goes high, and will stop if they all drop.   Note this is really cosmetic only (with the tab colour changing red to green) and start/stop logging, and data will be still be captured even if all the control line are low.  But unless the channel is seen to 'start', some functionality may not work correctly such as capture file name roll over.