Instruction manual

Serial Port Expansion Cards

Modern PCs are supplied with two serial ports; one is a 9-pin male and the other a 25-pin female. Typically they are

designated as COM1 and COM2 respectively. If a mouse is supplied, it is connected in one of the following ways;

directly into the 9 pin serial connector, into its own “PS/2” style jack, into the 25 pin connector via a 9 pin to 25 pin

adapter, or into its own specialized card input jack. Assuming the mouse is hooked either to COM1 or COM2, only

one COM port is free for accessories. There is a market for USB devices, which in principal can offer functions in

this area. USB is a serial bus standard, which allows multiple devices (mice, keyboards, and joysticks) to be

connected to a single wire. However, since the USB market is small, proprietary and expensive, we do not intend to

support it in the foreseeable future, so it will not be discussed here.

Depending upon the devices attached to the PC, you will have particular needs with respect to I/O ports. First, the

Observatory controller requires 1 COM port- our standard port is COM2, although all our software will support

COM1 through COM9. CCD cameras typically use a LPT (printer) port, but some require a serial port and others

require both. The Telescope mount will consume either another COM port or an LPT port depending upon the

particular mount design.

Modems can either use an existing port, or can supply one of their own- depending upon the modem’s design.

Internal modems always supply their own, often as COM3 so as not to conflict with COM1 and COM2 as supplied

by the main system board. External modems always need a 9 or 25 pin COM port, thereby using one supplied by

the main system board or expansion card.

If your system only requires 1 LPT port for the CCD, 1 COM port for the Observatory and 1 COM port for the

Telescope mount, it may be possible to set the system up without requiring additional COM/LPT port cards. The

key is to use an internal modem (if you need a modem) and ensure your computer main board accepts a PS/2 style

mouse (most motherboards less than 2 years old do). If your motherboard supports PS/2 mice, it might be just a

matter of purchasing a PS/2 style mouse, plugging it in and enabling PS/2 mouse functions via main system board

jumpers or CMOS settings. Windows 3.1 and up will directly recognize PS/2 mice (as will alternative operating

systems like Linux or BeOS). If your main system board does not support PS/2 mice, or you don’t have a sufficient

quantity of COM and LPT ports, you will most likely need an expansion card.

There are many variations of COM/LPT expansion cards, offering a wide array of port combinations, data rate

capabilities and connector styles. Costs will range from $10 for old style cards pulled from XT/AT machines to

several hundred dollars for the latest, most capable versions. In our experience, cards, which mix 2 or more COM

ports plus 1 or more LPT ports, are the most effective in this application. (Don’t ignore the XT/AT pulls out of

hand; they could do exactly what you need. If you buy one, be sure you know how to configure it!) We purchase

cards in the $40 to $150 price range, from Jameco Electronics (www.jameco.com) and JDR (www.jdr.com). We

select cards which provide additional 9 pin and 25 pin ports, or those with a large cable connector from which

dangle individual, short cables with 9 pin and 25 pin connectors. The particular UART chips employed on the card

are of little concern in this application and can be ignored unless you have special requirements. If you search

around, you may run into the 4 or more port serial boards, costing in the many hundreds to thousands of dollars.

These cards are very capable and are specially designed to not “over consume” system resources as discussed below.

Unless your needs are stringent or you’ve exhausted other avenues, leave these fancy cards as a final alternative.

Although most of the COM/LPT expansion cards will be “ISA” bus, you will some PCI bus cards. The

ads/salespeople will claim they are “faster”- certainly they are more expensive, but consider the limiting factor in the

communications link is the device sending the data. PCI Vs ISA offer little or no performance difference with

respect to speed with which Telescopes or DEVICE transmit on COM/LPT ports. On the other hand, if you are

servicing an ISDN modem, a high throughput card is preferred.

Our experience is, the most important factor in selecting a card is the configurability. Specifically, each COM and

LPT port on a card will utilize one of a limited number of IRQ “slots” on the main system board. Many other PC

functions also use them, typically leaving only several available for expansion card use. Consequently, it is often

the case that on a fancy, new multi port card there are one or more of the ports, which are useless because of a lack