In General, it all depends upon the context.

Data rates (or baud rates) are highly system / context dependent. It is impossible for Greenleaf Software or its suppliers to know exactly how fast one of our products or solutions will perform in your specific system. Thus our data rate specification is the maximum speed each port on the product (or an application built using out software) can achieve in an ideal, yet realistic, context. Our specified maximum baud rate is related to the hardware, UART chipset, and the observation of a great many real-world test conditions.

IMPORTANT RE: QUATECH

When assessing the capabilities of Quatech products it is important to remember that any given port on the product is capable of the specified maximum data rate at the hardware level, and the device driver lefel. As far as the device drivers are concerned, all ports are independent and equally capable.

Dependencies

Regardless of how careful we are to use discretion in stating maximum baud rates, there are many factors that are beyond our control. In addition, the specifications EIA-232, EIA-422, and EIA-485 (commonly referred to as RS-232, etc.) govern physical and electrical means and tolerances for such things as connector geometry, maximum cable length, capacitance per ft. between wires, grounding plus shield, voltages and rise/fall times for the bus. Note that there are many inexpensive pre-built cables that may or may not meet the associated specifications, and since one can buy cable in bulk, we've seen developers and users of hardware who get into trouble with excessive cable length, poor ground or signal connection, and other physical matters that you might not expect to cause problems. In all cases, maximum baud rate in a set of conditions can be less than our specified buad rate if, for instance, capacitive load on the drivers is high due to cable length or design.

Here are just some of the many factors that can materially affect the baud rate at which your particular application, use of hardware, etc.

• Processor speed
• Degree of load placed on the card's outputs (reactive, capacitive)
• Operating system, SP level, and serial driver version and make
• Software load: Processors run threads, not programs, and since many systems are either multiprocessor or use Intel's Hyperthreading© technology, loading can depend upon a very large number of factors.
• Efficiency of the software application using a particular port.
• For ViewComm System users, proper driver installation is a must and will generally limit throughput to spcified maximums because the VCS software shuts down the FIFOs in order to manage accurate timestamps
• Proper use of hardware handshaking (RTS/CTS or DTR/DSR) or software flow control (XON/XOFF)
• How the port hardware (UART) is connected to the machine. Windows 95 and above virtualizes most serial ports connected to the computer via USB, Ethernet, etc., and so the baud rate limit is affected by the loading and performance of the connecting link technology and speed, and hardware involved.

Third Party Stuff

When USB or Ethernet products such as device servers, there will generally be third-party controller chips and their associated drivers and operating system components sitting between the serial device drivers and hardware from Greenleaf Software's vendors; sometimes these items have unpredictable effects on throughput.

Special Note re: Quatech Surge Suppressors (IND)

As noted above, one of the factors that can affect baud rate is capacitive loads. When the ports are equipped with surge suppressors, those suppressors add enough capacitance to prevent the transceivers from reaching speeds as high as the standard cards can achieve. Typically, Quatech products with the surge suppression option are limited to 115.2 kbps maximum under optimal conditions. As with the standard cards, this value was determined by observing the cards' performance in a variety of testing scenarios.

If you have questions about data rates and how Quatech boards will perform in your system, we encourage you to contact Greenleaf Software using the Support Request form at http://www.GreenleafSoft.com/ProblemReport.asp. We have a great many years experience with both general serial communications and with Quatech hardware, and if we can't answer your question we'll promptly get you in touch with someone who can.