TECH NOTES


USE OF COMPUTER PORTS

By Dave Pruett, K8CC

When a new user first installs NA, they are quite often thrilled at their first experience of using the program. The joys of effortlessly logging QSOs, dupe/mult checking, and especially printing the final logs ready to turn in is enough to make even the most jaded pencil-pushing contester want to go find a contest to operate. However, the real benefits and power of modern logging programs like NA come when the computer is interfaced to the rest of the station, allowing additional features and the automation of many station functions.

This month's topic for DATOM TECH NOTES is a discussion of the computer ports which are used to interface to the station. Most MS-DOS computers have two types of ports that are useful for station interfacing. The first type of port is called a PARALLEL PORT, where the data comes out of the computer in parallel eight bits at a time. This type of port is also sometimes referred to as a LPT PORT, where "LPT" is a contraction for "line printer". Indeed, the most common usage for a parallel port is connection to a printer. The second type of port is called a SERIAL PORT, where the data comes out of the computer serially one bit at a time. This type of port is also sometimes referred to as a COM PORT, where "COM" is an abbreviation for "communications". A serial port is often used for communications where data arrives in sequence, perhaps from a modem or TNC.

The architecture of most MS-DOS computers provides for up to three LPT ports and up to four COM ports. When the computer boots up, it looks in certain internal addresses and counts up the number of ports it finds. The location of these ports is tabulated in the BIOS DATA TABLE in the computer's memory. Computer programs such as NA or CVB can use this information to determine which ports are available and configure themselves accordingly to use the ports. Each port must have its own unique address, or else a PORT CONFLICT occurs and the ports will not operate correctly.

Another issue about ports concerns the INTERRUPT REQUEST LINES, or IRQs. Each serial port must have its own IRQ to function correctly or else an IRQ CONFLICT occurs. NA does not require LPTs to have an IRQ to function correctly, but if a LPT port has an IRQ assigned to it, it must not be shared with another device. Other types of programs such as print spoolers might require an LPT used with a printer to have an IRQ assigned to it.

IRQs can be a real limitation because there are only a certain number implemented in a MS-DOS computer. Old 8088 computers had only eight IRQs (0 - 7), while 80286 and later machines have this expanded to 16 (0 - 15). Certain of these IRQs have to be used by the computer itself - these are described in the NA manual. A bus mouse requires and IRQ, as do most sound cards. Of the remaining IRQs, an unofficial convention has evolved. In most cases, COM1 is assigned to IRQ4, COM2 is assigned to IRQ3, LPT1 is assigned to IRQ7 and LPT2 is assigned to IRQ5. If COM3 or COM4 is installed, it typically must operate off of a "high IRQ" (i.e., above IRQ7), but not all serial cards will operate with high IRQs. If you don't need IRQs on your LPT ports then disconnect them (typically by removing a jumper on the LPT card) and use the IRQs for COM3/4. This is the way the logging computers are set up at K8CC (all six of them!) with COM3 on IRQ5 and COM4 on IRQ7.

There a number of uses for both COM and LPT ports in interfacing to your station. With only two exceptions, a certain type of port is required. Here is a list of the functions:

LPT

CW keying
CVB control interface
External voicekeyer control
External band control
Two-radio control
W9XT Contest Card

COM

CW keying
CVB control interface
Radio-Computer interface
TNC
NA Network connections
RS-232 rotator

Certain combinations can successfully share a single port. For example, CW keying or the CVB interface can share a COM port with one of the other COM functions listed. On the LPT side, CW keying can share a port with one of the other functions listed. Further combinations of LPT functions requires careful selection - the limitations for such combinations are described in the NA manual.

The experience at K8CC has been that you'll run out of COM ports before you run out of LPT ports, so use LPTs whenever possible. A single LPT port can do CW keying, two-radio control and EITHER band control or voicekeyer control. A W9XT Contest Card can do CW keying in addition to its voicekeyer functions, but cannot do more because the LPT pins are not brought out to the external connector. A second (or third) LPT card can do external band control for even two radios for a two-radio single op.

More than two COM ports are necessary for elaborate setups. A single-op assisted station might need two COMs for radio-computer interfaces, another for the TNC, and the last can be used for a rotator, for keying, or a spare. In multi-ops using an NA Network, each station is likely to need one COM for a radio-computer interface, and two for a LINK network (although only one is required for a LOOP network). At least one station in the network needs a TNC connection, so that computer will need four COMs.

One last hint. Make sure your serial card can provide the IRQ flexibility you will need for COM3/4. Some cards have COM3 permanently connected to IRQ4 and COM4 to IRQ3. These cards cannot be used with NA for COM3/4. Most modern cards have come to grips with the IRQ shortage and can be used with any valid IRQ, even the "high" IRQs. Check before you buy!

Next time, we'll discuss the setup and troubleshooting of serial ports. See you then!


DATOM Tech Notes:

DATOM TECH NOTES is a feature of the DATOM Engineering Web Page, covering technical topics applicable to the NA Contest Logging or Contest Voice Blaster programs. We would welcome your comments, and suggestions for topics to be covered in future editions.

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